# Yabasic

## Chapter 1. Introduction

## About this document

This document describes yabasic. You will find information about the yabasic interpreter (the program yabasic under Unix or yabasic.exe under Windows) as well as the language (which is, of course, a sort of basic) itself.

This document applies to version 2.760 of yabasic

However, this document does not contain the latest news about yabasic or a FAQ. As such information tends to change rapidly, it is presented online only at www.yabasic.de.

Although basic has its reputation as a language for beginning programmers, this is not an introduction to programming at large. Rather this text assumes, that the reader has some (moderate) experience with writing and starting computer programs.

## About yabasic

yabasic is a traditional basic interpreter. It understands most of the typical basic-constructs, like `goto`, `gosub`, line numbers, `read`, `data` or string-variables with a trailing '`$`'. But on the other hand, yabasic implements some more advanced programming-constructs like subroutines or libraries (but not objects). yabasic works much the same under Unix and Windows.

yabasic puts emphasis on giving results quickly and easily; therefore simple commands are provided to open a graphic window, print the graphics or control the console screen and get keyboard or mouse information. The example below opens a window, draws a circle and prints the graphic:

    open window 100,100
    open printer
    circle 50,50,40
    text 10,50,"Press any key to get a printout"
    clear screen
    inkey$
    close printer
    close window

This example has fewer lines, than it would have in many other programming languages. In the end however yabasic lacks behind more advanced and modern programming languages like C++ or Java. But as far as it goes it tends to give you results more quickly and easily.

## Chapter 2. The yabasic-program under Windows

## Starting yabasic

Once, yabasic has been set up correctly, there are three ways to start it:

1. Rightclick on your desktop: The desktop menu appears with a submenu named new. From this submenu choose yabasic. This will create a new icon on your desktop. If you rightclick on this icon, its context menu will appear; choose Execute to execute the program.

2. As a variant of the way described above, you may simply create a file with the ending `.yab` (e.g. with your favorite editor). Everything else then works as described above.

3. From the start-menu: Choose yabasic from your start-menu. A console-window will open and you will be asked to type in your program. Once you are finished, you need to type `return` twice, and yabasic will parse and execute your program.

   ### Note

   This is not the preferred way of starting yabasic ! Simply because the program, that you have typed, can not be saved and will be lost inevitably ! There is no such thing as a `save`-command and therefore no way to conserve the program, that you have typed. This mode is only intended for quick hacks, and short programs.

## Options

Under Windows yabasic will mostly be invoked by double-clicking on an appropriate icon; this way you do not have a chance to specify any of the commandline options below. However, advanced users may add some of those options to the appropriate entries in the registry.

All the options below may be abbreviated, as long as the abbreviation does not become ambiguous. For example, you may write `-e` instead of `-execute`.

`-help` or `-?`

  Prints a short help message, which itself describes two further help-options.

`-version`

  Prints the version of yabasic.

`-geometry +`X-POSITION`+`Y-POSITION``

  Sets the position of the graphic window, that is opened by `open window` (the size of this window, of course, is specified within the `open window`-command). An example would be `-geometry +20+10`, which would place the graphic window 10 pixels below the upper border and 20 pixels right of the left border of the screen. This value cannot be changed, once yabasic has been started.

`-font `NAME-OF-FONT``

  Name of the font, which will be used for graphic-text; can be any of `decorative, dontcare, modern, roman, script, swiss`. You may append a fontsize (measured in pixels) to any of those fontnames; for example `-font swiss30` chooses a swiss-type font with a size of 30 pixels.

`-bind `NAME-OF-STANDALONE-PROGRAM``

  Create a standalone program (whose name is specified by `NAME-OF-STANDALONE-PROGRAM`) from the yabasic-program, that is specified on the commandline. See the section about creating a standalone-program for details.

`-execute `A-PROGRAM-AS-A-SINGLE-STRING``

  With this option you may specify some yabasic-code to be executed rigth away.This is useful for very short programs, which you do not want to save within a file. If this option is given, yabasic will not read any code from a file. Let's say, you have forgotten some of the square numbers between 1 and 10; in this case the command `yabasic -e 'for a=1 to 10:print a*a:next a'` will give you the answer immediately.

`-infolevel `INFOLEVEL``

  Change the infolevel of yabasic, where `INFOLEVEL` can be one of `debug`, `note`, `warning`, `error` and `fatal` (the default is `warning`). This option changes the amount of debugging-information yabasic produces. However, normally only the author of yabasic (me !) would want to change this.

`-doc `NAME-OF-A-PROGRAM``

  Print the embedded documentation of the named program. The embedded documentation of a program consists of all the comments within the program, which start with the special keyword `doc`. This documentation can also be seen by choosing the corresponding entry from the context-menu of any yabasic-program.

`-librarypath `DIRECTORY-WITH-LIBRARIES``

  Change the directory, wherein libraries will be searched and imported (with the `import`-command). See also `this entry` for more information about the way, libraries are searched.

## The context Menu

Like every other icon under Windows, the icon of every yabasic-program has a context menu offering the most frequent operations, that may be applied to a yabasic-program.

Execute

  This will invoke yabasic to execute your program. The same happens, if you doubleclick on the icon.

Edit

  notepad will be invoked, allowing you to edit your program.

View docu

  This will present the embedded documentation of your program. Embedded documentation is created with the special comment `doc`.

## Chapter 3. The yabasic-program under Unix

## Starting yabasic

If your system administrator (vulgo root) has installed yabasic correctly, there are three ways to start it:

1. You may use your favorite editor (emacs, vi ?) to put your program into a file (e.g. `foo`). Make sure that the very first line starts with the characters '`#!`' followed by the full pathname of yabasic (e.g. '`#!/usr/local/bin/yabasic`'). This she-bang-line ensures, that your Unix will invoke yabasic to execute your program (see also the entry for the hash-character). Moreover, you will need to change the permissions of your yabasic-program `foo`, e.g. `chmod u+x foo`. After that you may invoke yabasic to invoke your program by simply typing `foo` (without even mentioning yabasic). However, if your `PATH`-variable does not contain a single dot ('`.`') you will have to type the full pathname of your program: e.g. `/home/ihm/foo` (or at least `./foo`).

2. Save your program into a file (e.g. `foo`) and type `yabasic foo`. This assumes, that the directory, where yabasic resides, is contained within your `PATH`-variable.

3. Finally your may simply type `yabasic` (maybe it will be necessary to include its full pathname). This will make yabasic come up and you will be asked to type in your program. Once you are finished, you need to type `return` twice, and yabasic will parse and execute your program.

   ### Note

   This is not the preferred way of starting yabasic ! Simply because the program, that you have typed, can not be saved and will be lost inevitably ! There is no such thing as a `save`-command and therefore no way to conserve the program, that you have typed. This mode is only intended for quick hacks, and short programs, i.e. for using yabasic as some sort of fancy desktop calculator.

## Options

yabasic accepts a number of options on the commandline. All these options below may be abbreviated, as long as the abbreviation does not become ambigous. For example you may write `-e` instead of `-execute`.

`-help` or `-?`

  Prints a short help message, which itself describes two further help-options.

`-version`

  Prints the version of yabasic.

`-fg `FOREGROUND-COLOR`` or `-foreground `FOREGROUND-COLOR``

  Define the foreground color for the graphics-window (that will be opened with `open window`). The usual X11 colornames, like red, green, … are accepted. This value cannot be changed, once yabasic has been started.

`-bg `BACKGROUND-COLOR`` or `-background `BACKGROUND-COLOR``

  Define the background color for the graphics-window. The usual X11 colornames are accepted. This value cannot be changed, once yabasic has been started.

`-geometry +`X-POSITION`+`Y-POSITION``

  Sets the position of the graphic window, that is opened by `open window` (the size of this window, of course, is specified with the `open window`-command). An example would be `+20+10`, which would place the graphic window 10 pixels below the upper border and 20 pixels right of the left border of the screen. Note, that the size of the window may not be specified here (well it may, but it will be ignored anyway). This value cannot be changed, once yabasic has been started.

`-display `BACKGROUND-COLOR``

  Specify the display, where the graphics window of yabasic should appear. Normally, however this value will be already present within the environment variable `DISPLAY`.

`-font `NAME-OF-FONT``

  Name of the font, which will be used for text within the graphics window.

`-execute `A-PROGRAM-AS-A-SINGLE-STRING``

  With this option you may specify some yabasic-code to be executed rigth away.This is useful for very short programs, which you do not want to save to a file. If this option is given, yabasic will not read any code from a file. E.g.

      yabasic -e 'for a=1 to 10:print a*a:next a'

  prints the square numbers from 1 to 10.

`-bind `NAME-OF-STANDALONE-PROGRAM``

  Create a standalone program (whose name is specified by `NAME-OF-STANDALONE-PROGRAM`) from the yabasic-program, that is specified on the commandline. See the section about creating a standalone-program for details.

`-infolevel `INFOLEVEL``

  Change the infolevel of yabasic where `INFOLEVEL` can be one of `debug`, `note`, `warning`, `error` and `fatal` (the default is `warning`). This option changes the amount of debugging-information yabasic produces. However, normally only the author of yabasic (me !) would want to change this.

`-doc `NAME-OF-A-PROGRAM``

  Print the embedded documentation of the named program. The embedded documentation of a program consists of all the comments within the program, which start with the special keyword `doc`.

`-librarypath `DIRECTORY-WITH-LIBRARIES``

  Change the directory from which libraries will be imported (with the `import`-command). See also this entry for more information about the way, libraries will be searched.

## Setting defaults

If you want to set some options once for all, you may put them into your X-Windows resource file. This is usually the file `.Xresources` or some such within your home directory (type `man X` for details).

Here is a sample section, which may appear within this file:

    yabasic*foreground: blue
    yabasic*background: gold
    yabasic*geometry: +10+10
    yabasic*font: 9x15

This will set the foreground color of the graphic-window to blue and the background color to gold. The window will appear at position 10,10 and the text font will be 9x15.

## Chapter 4. Some features of yabasic, explained by topic

This chapter has sections for some of the major features of yabasic and names a few commands related with each area. So, depending on your interest, you find the most important commands of this area named; the other commands from this area may then be discovered through the links in the see also-section.

## `print`, `input` and others

The `print`-command is used to put text on the text screen. Here, the term text screen stands for your terminal (under Unix) or the console window (under Windows).

At the bottom line, `print` simply outputs its argument to the text window. However, once you have called `clear screen` you may use advanced features like printing colors or copying areas of text with `getscreen$` or `putscreen`.

You may ask the user for input with the `input`-command; use `inkey$` to get each key as soon as it is pressed.

## Control statements: loops, `if` and `switch`

Of course, yabasic has the `goto`- and `gosub`-statements; you may go to a `label` or a line number (which is just a special kind of label). `goto`, despite its bad reputation ([`goto` considered harmful]), has still its good uses; however in many cases you are probably better off with loops like `repeat`-`until`, `while`-`wend` or `do`-`loop`; you may leave any of these loops with the `break`-statement or start the next iteration immediately with `continue`.

Decisions can be made with the `if`-statement, which comes either in a short and a long form. The short form has no `then`-keyword and extends up to the end of the line. The long form extends up to the final `endif` and may use some of the keywords `then` (which introduces the long form), `else` or `elsif`.

If you want to test the result of an expression against many different values, you should probably use the `switch`-statement.

## Drawing and painting

You need to call `open window` before you may draw anything with either `line`, `circle`, `rectangle` or `triangle`; all of these statements may be decorated with `clear` or `fill`. If you want to change the colour for drawing, use `colour`. Note however, that there can only be a single window open at any given moment in time.

Everything you have drawn can be send to your printer too, if you use the `open printer` command.

To allow for some (very) limited version of animated graphics, yabasic offers the commands `getbit$` and `putbit`, which retrieve rectangular regions from the graphics-window into a string or vice versa.

If you want to sense mouse-clicks, you may use the `inkey$`-function.

## Reading from and writing to files

Before you may read or write a file, you need to `open` it; once you are done, you should `close` it. Each open file is designated by a simple number, which might be stored within a variable and must be supplied if you want to access the file. This is simply done by putting a hash ('`#`') followed by the number of the file after the keyword `input` (for reading from) or `print` (for writing to a file) respectively.

If you need more control, you may consider reading and writing one byte at a time, using the multi-purpose commands `peek` and `poke`.

## Subroutines and Libraries

The best way to break any yabasic-program into smaller, more manageable chunks are subroutines and libraries. They are yabasic's most advanced means of structuring a program.

Subroutines are created with the command `sub`. they accept parameters and may return a value. Subroutines can be called much like any builtin function of yabasic; therefore they allow to extend the language itself.

Once you have created a set of related subroutines and you feel that they could be useful in other programs too, you may collect them into a library. Such a library is contained within a separate file and may be included in any of your programs, using the keyword `import`.

## String processing

yabasic has the usual functions to extract parts from a string: `left$`, `mid$` and `right$`. Note, that all of them can be assigned to, i.e. they may change part of a string.

If you want to split a string into tokens you should use the functions `token` or `split`.

There is quite a bunch of other string-processing functions like `upper$` (converting to upper case), `instr` (finding one string within the other), `chr$` (converting an ascii-code into a character), `glob` (testing a string against a pattern) and more. Just follow the links.

## Arithmetic

Yabasic handles numbers and arithmetic: You may calculate trigonometric functions like `sin` or `atan`, or logarithms (with `log`). Bitwise operations, like `and` or `or` are available as well `min` or `max` (calculate the minimum or maximum of its argument) or `mod` or `int` (reminder of a division or integer part or a number).

## Data and such

You may store data within your program within `data`-statements; during execution you will probably want to `read` it into arrays, which must have been `dim`ed before.

## Other interesting commands.

- Yabasic programs may start other programs with the commands `system` and `system$`.

- `peek` and `poke` allow to get and set internal information; either for the operating system (i.e. Unix or Windows) or yabasic itself.

- The current time or date can be retrieved with (guess what !) `time$` and `date$`.

## Chapter 5. All commands and functions of yabasic listed by topic

### Number processing and conversion

abs()
  returns the absolute value of its numeric argument
acos()
  returns the arcus cosine of its numeric argument
and()
  the bitwise arithmetic `and`
asin()
  returns the arcus sine of its numeric argument
atan()
  returns the arctangent of its numeric argument
bin$()
  converts a number into a sequence of binary digits
cos()
  return the cosine of its single argument
dec()
  convert a base 2 or base 16 number into decimal form
eor()
  compute the bitwise exclusive or of its two arguments
euler
  another name for the constant `2.71828182864`
exp()
  compute the exponential function of its single argument
frac()
  return the fractional part of its numeric argument
int()
  return the integer part of its single numeric argument
log()
  compute the natural logarithm
max()
  return the larger of its two arguments
min()
  return the smaller of its two arguments
mod()
  compute the remainder of a division
or()
  arithmetic or, used for bit-operations
pi
  a constant with the value `3.14159`
ran()
  return a random number
sig()
  return the sign of its argument
sin()
  return the sine of its single argument
sqr()
  compute the square of its argument
sqrt()
  compute the square root of its argument
tan()
  return the tangent of its argument
xor()
  compute the exclusive or
** or ^
  raise its first argument to the power of its second

### Conditions and control structures

and
  logical and, used in conditions
break
  breaks out of a switch statement or a loop
case
  mark the different cases within a `switch`-statement
continue
  start the next iteration of a `for`-, `do`-, `repeat`- or `while`-loop
default
  mark the default-branch within a `switch`-statement
do
  start a (conditionless) `do-loop`
else
  mark an alternative within an `if`-statement
elsif
  starts an alternate condition within an `if`-statement
end
  terminate your program
endif
  ends an `if`-statement
false
  a constant with the value of 0
fi
  another name for `endif`
for
  starts a `for`-loop
gosub
  continue execution at another point within your program (and return later)
goto
  continue execution at another point within your program (and never come back)
if
  evaluate a condition and execute statements or not, depending on the result
label
  mark a specific location within your program for `goto`, `gosub` or `restore`
loop
  marks the end of an infinite loop
next
  mark the end of a for loop
not
  negate an expression; can be written as `!`
on gosub
  jump to one of multiple `gosub`-targets
on goto
  jump to one of many `goto`-targets
on interrupt
  change reaction on keyboard interrupts
logical or
  logical or, used in conditions
pause
  pause, sleep, wait for the specified number of seconds
repeat
  start a `repeat`-loop
return
  return from a subroutine or a gosub
sleep
  pause, sleep, wait for the specified number of seconds
switch
  select one of many alternatives depending on a value
then
  tell the long from the short form of the `if`-statement
true
  a constant with the value of 1
until
  end a `repeat`-loop
wait
  pause, sleep, wait for the specified number of seconds
wend
  end a `while`-loop
while
  start a `while`-loop
:
  separate commands from each other

### Data keeping and processing

arraydim()
  returns the dimension of the array, which is passed as an array reference
arraysize()
  returns the size of a dimension of an array
data
  introduces a list of data-items
dim
  create an array prior to its first use
read
  read data from `data`-statements
redim
  create an array prior to its first use. A synonym for `dim`
restore
  reposition the `data`-pointer

### String processing

asc()
  accepts a string and returns the position of its first character within the ascii charset
chr$()
  accepts a number and returns the character at this position within the ascii charset
glob()
  check if a string matches a simple pattern
hex$()
  convert a number into hexadecimal
instr()
  searches its second argument within the first; returns its position if found
left$()
  return (or change) left end of a string
len()
  return the length of a string
lower$()
  convert a string to lower case
ltrim$()
  trim spaces at the left end of a string
mid$()
  return (or change) characters from within a string
right$()
  return (or change) the right end of a string
split()
  split a string into many strings
str$()
  convert a number into a string
token()
  split a string into multiple strings
trim$()
  remove leading and trailing spaces from its argument
upper$()
  convert a string to upper case
val()
  converts a string to a number

### File operations and printing

at()
  can be used in the `print`-command to place the output at a specified position
beep
  ring the bell within your computer; a synonym for `bell`
bell
  ring the bell within your computer (just as `beep`)
clear screen
  erases the text window
close
  close a file, which has been opened before
close printer
  stops printing of graphics
print color
  print with color
print colour
  see `print color`
eof
  check, if an open file contains data
getscreen$()
  returns a string representing a rectangular section of the text terminal
inkey$
  wait, until a key is pressed
input
  read input from the user (or from a file) and assign it to a variable
line input
  read in a whole line of text and assign it to a variable
open
  open a file
open printer
  open printer for printing graphics
print
  Write to terminal or file
putscreen
  draw a rectangle of characters into the text terminal
reverse
  print reverse (background and foreground colors exchanged)
screen
  as `clear screen` clears the text window
seek()
  change the position within an open file
tell
  get the current position within an open file
using
  Specify the format for printing a number
#
  either a comment or a marker for a file-number
@
  synonymous to `at`
;
  suppress the implicit newline after a `print`-statement

### Subroutines and libraries

end sub
  ends a subroutine definition
export
  mark a function as globally visible
import
  import a library
local
  mark a variable as local to a subroutine
numparams
  return the number of parameters, that have been passed to a subroutine
return
  return from a subroutine or a gosub
static
  preserves the value of a variable between calls to a subroutine
step
  specifies the increment step in a for-loop
sub
  declare a user defined subroutine

### Other commands

bind()
  Binds a yabasic-program and the yabasic-interpreter together into a standalone program.
compile
  compile a string with yabasic-code on the fly
date$
  returns a string with various components of the current date
doc
  special comment, which might be retrieved by the program itself
docu$
  special array, containing the contents of all docu-statement within the program
error
  raise an error and terminate your program
execute$()
  execute a user defined subroutine, which must return a string
execute()
  execute a user defined subroutine, which must return a number
exit
  terminate your program
pause
  pause, sleep, wait for the specified number of seconds
peek
  retrieve various internal informations
peek$
  retrieve various internal string-informations
poke
  change selected internals of yabasic
rem
  start a comment
sleep
  pause, sleep, wait for the specified number of seconds
system$()
  hand a statement over to your operating system and return its output
system()
  hand a statement over to your operating system and return its exitcode
time$
  return a string containing the current time
to
  this keyword appears as part of other statements
wait
  pause, sleep, wait for the specified number of seconds
//
  starts a comment
:
  separate commands from each other

### Graphics and printing

backcolor
  specify the colour for subsequent drawing of the background
box
  draw a rectangle. A synonym for `rectangle`
circle
  draws a circle in the graphic-window
clear
  Erase `circle`s, `rectangle`s or `triangles`s
clear window
  clear the graphic window and begin a new page, if printing is under way
close curve
  close a curve, that has been drawn by the `line`-command
close window
  close the graphics-window
colour
  specify the colour for subsequent drawing
dot
  draw a dot in the graphic-window
fill
  draw a filled `circle`s, `rectangle`s or `triangle`s
getbit$()
  return a string representing the bit pattern of a rectangle within the graphic window
line
  draw a line
mouseb
  extract the state of the mousebuttons from a string returned by `inkey$`
mousemod
  return the state of the modifier keys during a mouseclick
mousex
  return the x-position of a mouseclick
mousey
  return the y-position of a mouseclick
new curve
  start a new curve, that will be drawn with the `line`-command
open window
  open a graphic window
putbit
  draw a rectangle of pixels into the graphic window
rectangle
  draw a rectangle
triangle
  draw a triangle
text
  write text into your graphic-window
window origin
  move the origin of a window

## Chapter 6. All commands and functions of yabasic grouped alphabetically

### A

## Name

abs() — returns the absolute value of its numeric argument

## Synopsis

    y=abs(x)

## Description

If the argument of the `abs`-function is positive (e.g. 2) it is returned unchanged, if the argument is negative (e.g. -1) it is returned as a positive value (e.g. 1).

## Example

    print abs(-2),abs(2)

This example will print `2 2`

## See also

`sig`

## Name

acos() — returns the arcus cosine of its numeric argument

## Synopsis

    x=acos(angle)

## Description

`acos` is the arcus cosine-function, i.e. the inverse of the `cos`-function. Or, more elaborate: It Returns the angle (in radian, not degree !), which, fed to the cosine-function will produce the argument passed to the `acos`-function.

## Example

    print acos(0.5),acos(cos(pi))

This example will print `1.0472 3.14159` which are π/3 and π respectively.

## See also

`cos`, `asin`

## Name

and — logical and, used in conditions

## Synopsis

    if (a and b) …
    while (a and b) …

## Description

Used in conditions (e.g within `if`, `while` or `until`) to join two expressions. Returns `true`, if and only if its left and right argument are both `true` and `false` otherwise.

Note, that logical shortcuts may take place.

## Example

    input "Please enter a number" a
    if (a>=1 and a<=9) print "your input is between 1 and 9"

## See also

`or`,`not`

## Name

and() — the bitwise arithmetic `and`

## Synopsis

    x=and(a,b)

## Description

Used to compute the bitwise `and` of both its argument. Both arguments are treated as binary numbers (i.e. a series of 0 and 1); a bit of the resulting value will then be 1, if both arguments have a 1 at this position in their binary representation.

Note, that both arguments are silently converted to integer values and that negative numbers have their own binary representation and may lead to unexpected results when passed to `and`.

## Example

    print and(6,3)

This will print `2`. This result is clear, if you note, that the binary representation of 6 and 3 are 110 and 011 respectively; this will yield 010 in binary representation or 2 as decimal.

## See also

`or`, `eor` and `not`

## Name

arraydim() — returns the dimension of the array, which is passed as an array reference

## Synopsis

    a=arraydim(b())

## Description

If you apply the `arraydim()`-function on a one-dimensional array (i.e. a vector) it will return `1`, on a two-dimensional array (i.e. a matrix) it will return 2, and so on.

This is mostly used within subroutines, which expect an array among their parameters. Such subroutines tend to use the `arraydim`-function to check, if the array which has been passed, has the right dimension. E.g. a subroutine to multiply two matrices may want to check, if it really is invoked with two 2-dimensional arrays.

## Example

    dim a(10,10),b(10)
    print arraydim(a()),arraydim(b())

This will print `2 1`, which are the dimension of the arrays `a()` and `b()`. You may check out the function `arraysize` for a full-fledged example.

## See also

`arraysize` and `dim`.

## Name

arraysize() — returns the size of a dimension of an array

## Synopsis

    x=arraysize(a(),b)

## Description

The `arraysize`-function computes the size of a specified dimension of a specified array. Here, size stands for the maximum number, that may be used as an index for this array. The first argument to this function must be an reference to an array, the second one specifies, which of the multiple dimensions of the array should be taken to calculate the size.

An Example involving subroutines: Let's say, an array has been declared as `dim a(10,20)` (that is a two-dimensional array or a matrix). If this array is passed as an array reference to a subroutine, this sub will not know, what sort of array has been passed. With the `arraydim`-function the sub will be able to find the dimension of the array, with the `arraysize`-function it will be able to find out the size of this array in its two dimensions, which will be 10 and 20 respectively.

Our sample array is two dimensional; if you envision it as a matrix this matrix has 10 lines and 20 columns (see the `dim`-statement above. To state it more formally: The first dimension (lines) has a size of 10, the second dimension (columns) has a size of 20; these numbers are those returned by `arraysize(a(),1)` and `arraysize(a(),2)` respectively. Refer to the example below for a typical usage.

## Example

    rem
    rem  This program adds two matrices elementwise.
    rem

    dim a(10,20),b(10,20),c(10,20)

    rem  initialization of the arrays a() and b()
    for y=1 to 10:for x=1 to 20
       a(y,x)=int(ran(4)):b(y,x)=int(ran(4))
    next x:next y

    matadd(a(),b(),c())

    print "Result:"
    for x=1 to 20
       for y=10 to 1 step -1
          print c(y,x)," ";
       next y
       print
    next x

    sub matadd(m1(),m2(),r())

       rem  This sub will add the matrices m1() and m2()
       rem  elementwise and store the result within r()
       rem  This is not very useful but easy to implement.
       rem  However, this sub excels in checking its arguments
       rem  with arraydim() and arraysize()

       local x:local y

       if (arraydim(m1())<>2 or arraydim(m2())<>2 or arraydim(r())<>2) then
          error "Need two dimensional arrays as input"
       endif

       y=arraysize(m1(),1):x=arraysize(m1(),2)
       if (arraysize(m2(),1)<>y or arraysize(m2(),2)<>x) then
          error "The two matrices cannot be added elementwise"
       endif

       if (arraysize(r(),1)<>y or arraysize(r(),2)<>x) then
          error "The result cannot be stored in the third argument"
       endif

       local xx:local yy
       for xx=1 to x
          for yy=1 to y
             r(yy,xx)=m1(yy,xx)+m2(yy,xx)
          next yy
       next xx

     end sub

## See also

`arraydim` and `dim`.

## Name

asc() — accepts a string and returns the position of its first character within the ascii charset

## Synopsis

    a=asc(char$)

## Description

The `asc`-function accepts a string, takes its first character and looks it up within the ascii-charset; this position will be returned. The `asc`-function is the opposite of the `chr$`-function. There are valid uses for `asc`, however, comparing strings (i.e. to bring them into alphabetical sequence) is not among them; in such many cases you might consider to compare strings directly with `<`, `=` and `>` (rather than converting a string to a number and comparing this number).

## Example

    input "Please enter a letter between 'a' and 'y': " a$
    if (a$<"a" or a$>"y") print a$," is not in the proper range":end
    print "The letter after ",a$," is ",chr$(asc(a$)+1)

## See also

`chr$`

## Name

asin() — returns the arcus sine of its numeric argument

## Synopsis

    angle=asin(x)

## Description

`acos` is the arcus sine-function, i.e. the inverse of the `sin`-function. Or, more elaborate: It Returns the angle (in radian, not degree !), which, fed to the sine-function will produce the argument passed to the `asin`-function.

## Example

    print asin(0.5),asin(sin(pi))

This will print `0.523599 -2.06823e-13` which is π and almost 0 respectively.

## See also

`sin`, `acos`

## Name

at() — can be used in the `print`-command to place the output at a specified position

## Synopsis

    clear screen
    …
    print at(a,b)
    print @(a,b)

## Description

The `at`-clause takes two numeric arguments (e.g. `at(2,3)`) and can be inserted after the `print`-keyword. `at()` can be used only if `clear screen` has been executed at least once within the program (otherwise you will get an error).

The two numeric arguments of the `at`-function may range from 0 to the width of your terminal minus 1, and from 0 to the height of your terminal minus 1; if any argument exceeds these values, it will be truncated accordingly. However, yabasic has no influence on the size of your terminal (80x25 is a common, but not mandatory), the size of your terminal and the maximum values acceptable within the `at`-clause may vary. To get the size of your terminal you may use the `peek`-function: `peek("screenwidth")` returns the width of your terminal and `peek("screenheight")` its height.

## Example

    clear screen
    maxx=peek("screenwidth")-1:maxy=peek("screenheight")-1
    for x=0 to maxx
      print at(x,maxy*(0.5+sin(2*pi*x/maxx)/2)) "*"
    next x

This example plots a full period of the sine-function across the screen.

## See also

`print`, `clear screen`, `color`

## Name

atan() — returns the arctangent of its numeric argument

## Synopsis

    angle=atan(a,b)
    angle=atan(a)

## Description

`atan` is the arctangent-function, i.e. the inverse of the `tan`-function. Or, more elaborate: It Returns the angle (in radian, not degree !), which, fed to the `tan`-function will produce the argument passed to the `atan`-function.

The `atan`-function has a second form, which accepts two arguments: `atan(a,b)` which is (mostly) equivalent to `atan(a/b)` except for the fact, that the two-argument-form returns an angle in the range -π to π, whereas the one-argument-form returns an angle in the range -π/2 to π/2. To understand this you have to be good at math.

## Example

    print atan(1),atan(tan(pi)),atan(-0,-1),atan(-0,1)

This will print `0.463648 2.06823e-13 -3.14159 3.14159` which is π/4, almost 0, -π and π respectively.

## See also

`tan`, `sin`

### B

## Name

color — change color for background of graphic window

## Synopsis

    backcolour red,green,blue
    backcolour "red,green,blue"

## Description

Change the color, that becomes visible, if any portion of the window is erased, e.g. after `clear window` or `clear line`. Note however, that parts of the window, that display the old background color will not change.

As with the `color`-command, the new background color can either be specified as a triple of three numbers or as a single string, that contains those three numbers sperated by commas.

## Example

    open window 255,255
    for x=10 to 235 step 10:for y=10 to 235 step 10
      	backcolour x,y,0
    	clear window
    	sleep 1
    next y:next x

This changes the background colour of the graphic window repeatedly and clears it every time, so that it is filled with the new background colour.

## See also

`open window`, `color`, `line`, `rectangle`, `triangle`, `circle`

## Name

backcolour — see `backcolor`

## Synopsis

    backcolour red,green,blue
    backcolour "red,green,blue"

## See also

`color`

## Name

beep — ring the bell within your computer; a synonym for `bell`

## Synopsis

    beep

## Description

The `bell`-command rings the bell within your computer once. This command is not a sound-interface, so you can neither vary the length or the height of the sound (technically, it just prints `\a`). `bell` is exactly the same as `beep`.

## Example

    beep:print "This is a problem ..."

## See also

`beep`

## Name

bell — ring the bell within your computer (just as `beep`)

## Synopsis

    bell

## Description

The `beep`-command rings the bell within your computer once. `beep` is a synonym for `bell`.

## Example

    print "This is a problem ...":beep

## See also

`bell`

## Name

bin$() — converts a number into a sequence of binary digits

## Synopsis

    hexadecimal$=bin$(decimal)

## Description

The `bin$`-function takes a single numeric argument an converts it into a string of binary digits (i.e. zeroes and ones). If you pass a negative number to `bin$`, the resulting string will be preceded by a '-'.

If you want to convert the other way around (i.e. from binary to decimal) you may use the `dec`-function.

## Example

    for a=1 to 100
      print bin$(a)
    next a

This example prints the binary representation of all digits between 1 and 100.

## See also

`hex$`, `dec`

## Name

bind() — Binds a yabasic-program and the yabasic-interpreter together into a standalone program.

## Synopsis

    bind("foo.exe")

## Description

The `bind`-command combines your own yabasic-program (plus all the libraries it does `import`) and the interpreter by copying them into a new file, whose name is passed as an argument. This new program may then be executed on any computer, even if it does not have yabasic installed.

Please see the section about creating a standalone-program for details.

## Example

    if (!peek("isbound")) then
      bind "foo"
      print "Successfully created the standalone executable 'foo' !"
      exit
    endif

    print "Hello World !"

This example creates a standalone program `foo` from itself.

## See also

The section about creating a standalone-program, the `peek`-function and the commandline options for Unix and Windows.

## Name

box — draw a rectangle. A synonym for `rectangle`

## Synopsis

    See the rectangle-command.

## Description

The `box`-command does exactly the same as the `rectangle`-command; it is just a synonym. Therefore you should refer to the entry for the `rectangle`-command for further information.

## Name

break — breaks out of a switch statement or a loop

## Synopsis

    break

## Description

`break` transfers control immediately outside the enclosing loop or switch statement. This is the preferred way of leaving a such a statement (rather than `goto`, which is still possible in most cases).

## Example

    for a=1 to 10
      break
      print "Hi"
    next a

    while(1)
      break
      print "Hi"
    wend

    repeat
      break
      print "Hi"
    until(0)

    switch 1
    case 1:break
    case 2:case 3:print "Hi"
    end switch

This example prints nothing at all, because each of the loops (and the `switch`-statement) does an immediate `break` (before it could print any "Hi").

## See also

`for`, `while`, `repeat` and `switch`.

### C

## Name

case — mark the different cases within a `switch`-statement

## Synopsis

    switch a
      case 1
      case 2
      …
    end switch

    …

    switch a$
      case "a"
      case "b"
      …
    end switch

## Description

Please see the `switch`-statement.

## Example

    input a
    switch(a)
      case 1:print "one":break
      case 2:print "two":break
      default:print "more"
    end switch

Depending on your input (a number is expected) this code will print `one` or `two` or otherwise `more`.

## See also

`switch`

## Name

chr$() — accepts a number and returns the character at this position within the ascii charset

## Synopsis

    character$=chr$(ascii)

## Description

The `chr$`-function is the opposite of the `asc`-function. It looks up and returns the character at the given position within the ascii-charset. It's typical use is to construct nonprintable characters which do not occur on your keyboard.

Nevertheless you won't use `chr$` as often as you might think, because the most important nonprintable characters can be constructed using escape-sequences using the \-character (e.g. you might use \n instead of `chr$(10)` wherever you want to use the newline-character).

## Example

    print "a",chr$(10),"b"

This will print the letters 'a' and 'b' in different lines because of the intervening newline-character, which is returned by `chr$(10)`.

## See also

`asc`

## Name

circle — draws a circle in the graphic-window

## Synopsis

    circle x,y,r
    clear circle x,y,r
    fill circle x,y,r
    clear fill circle x,y,r

## Description

The `circle`-command accepts three parameters: The x- and y-coordinates of the center and the radius of the circle.

Some more observations related with the `circle`-command:

- The graphic-window must have been opened already.

- The circle may well extend over the boundaries of the window.

- If you have issued `open printer` before, the circle will finally appear in the printed hard copy of the window.

- `fill circle` will draw a filled (with black ink) circle.

- `clear circle` will erase (or clear) the outline of the circle.

- `clear fill circle` or `fill clear circle` will erase the full area of the circle.

## Example

    open window 200,200

    for n=1 to 2000
      x=ran(200)
      y=ran(200)
      fill circle x,y,10
      clear fill circle x,y,8
    next n

This code will open a window and draw 2000 overlapping circles within. Each circle is drawn in two steps: First it is filled with black ink (`fill circle x,y,10`), then most of this circle is erased again (`clear fill circle x,y,8`). As a result each circle is drawn with an opaque white interior and a 2-pixel outline (2-pixel, because the radii differ by two).

## See also

`open window`, `open printer`, `line`, `rectangle`, `triangle`

## Name

clear — Erase `circle`s, `rectangle`s or `triangle`s

## Synopsis

    clear rectangle 10,10,90,90
    clear fill circle 50,50,20
    clear triangle 10,10,20,20,50,30

## Description

May be used within the `circle`, `rectangle` or `triangle` command and causes these shapes to be erased (i.e. be drawn in the colour of the background).

`fill` can be used in conjunction with and wherever the `fill`-clause may appear. Used alone, `clear` will erase the outline (not the interior) of the shape (circle, rectangle or triangle); together with `fill` the whole shape (including its interior) is erased.

## Example

    open window 200,200
    fill circle 100,100,50
    clear fill rectangle 10,10,90,90

This opens a window and draws a pacman-like figure.

## See also

`clear`, `circle`, `rectangle`, `triangle`

## Name

clear screen — erases the text window

## Synopsis

    clear screen

## Description

`clear screen` erases the text window (the window where the output of `print` appears).

It must be issued at least once, before some advanced screen-commands (e.g. `print at` or `inkey$`) may be called; this requirement is due to some limitations of the `curses`-library, which is used by yabasic under Unix for some commands.

## Example

    clear screen
    print "Please press a key : ";
    a$=inkey$
    print a$

The `clear screen` command is essential here; if it would be omitted, yabasic would issue an error ("`need to call 'clear screen' first`") while trying to execute the `inkey$`-function.

## See also

`inkey$`

## Name

clear window — clear the graphic window and begin a new page, if printing is under way

## Synopsis

    clear window

## Description

`clear window` clears the graphic window. If you have started printing the graphic via `open printer`, the `clear window`-command starts a new page as well.

## Example

    open window 200,200
    open printer "t.ps"

    for a=1 to 10
    if (a>1) clear window
    text 100,100,"Hallo "+str$(a)
    next a

    close printer
    close window

This example prints 10 pages, with the text "Hello 1", "Hello 2", … and so on. The `clear screen`-command clears the graphics window and starts a new page.

## See also

`open window`, `open printer`

## Name

close — close a file, which has been opened before

## Synopsis

    close filenum
    close # filenum

## Description

The `close`-command closes an open file. You should issue this command as soon as you are done with reading from or writing to a file.

## Example

    open "my.data" for reading as 1
    input #1 a
    print a
    close 1

This program opens the file `"my.data"`, reads a number from it, prints this number and closes the file again.

## See also

`open`

## Name

close curve — close a curve, that has been drawn by the `line`-command

## Synopsis

    new curve
    line to x1,y1
    …
    close curve

## Description

The `close curve`-command closes a sequence of lines, that has been drawn by repeated `line to`-commands.

## Example

    open window 200,200
    new curve
    line to 100,50
    line to 150,150
    line to 50,150
    close curve

This example draws a triangle: The three `line to`-commands draw two lines; the final line is however not drawn explicitly, but drawn by the `close curve`-command.

## See also

`line`, `new curve`

## Name

close printer — stops printing of graphics

## Synopsis

    close printer

## Description

The `close printer`-command ends the printing graphics. Between `open printer` and `close printer` everything you draw (e.g. circles, lines …) is sent to your printer. `close printer` puts an end to printing and will make your printer eject the page.

## Example

    open window 200,200
    open printer
    circle 100,100,50
    close printer
    close window

As soon as `close printer` is executed, your printer will eject a page with a circle on it.

## See also

`open printer`

## Name

close window — close the graphics-window

## Synopsis

    close window

## Description

The `close window`-command closes the graphics-window, i.e. it makes it disappear from your screen. It includes an implicit `close printer`, if a printer has been opened previously.

## Example

    open window 200,200
    circle 100,100,50
    close window

This example will open a window, draw a circle and close the window again; all this without any pause or delay, so the window will be closed before you may regard the circle..

## See also

`open window`

## Name

color — change color for any subsequent drawing-command

## Synopsis

    colour red,green,blue
    colour "red,green,blue"

## Description

Change the color, in which lines, dots, circles, rectangles or triangles are drawn. The `color`-command accepts three numbers in the range 0 … 255 (as in the first line of the synopsis above). Those numbers specify the intensity for the primary colors red, green and blue respectively. As an example `255,0,0` is red and `255,255,0` is yellow.

Alternatively you may specify the color with a single string (as in the second line of the synopsis above); this string should contain three numbers, separated by commas. As an example `"255,0,255"` would be violet. Using this variant of the `colour`-command, you may use symbolic names for colours:

    open window 100,100
    yellow$="255,255,0"
    color yellow$
    text 50,50,"Hallo"

, which reads much clearer.

## Example

    open window 255,255
    for x=10 to 235 step 10:for y=10 to 235 step 10
      	colour x,y,0
      	fill rectangle x,y,x+10,y+10
    next y:next x

This fills the window with colored rectangles. However, none of the used colours contains any shade of blue, because the `color`-command has always 0 as a third argument.

## See also

`open window`, `backcolor`, `line`, `rectangle`, `triangle`, `circle`

## Name

colour — see `color`

## Synopsis

    colour red,green,blue
    colour "red,green,blue"

## See also

`color`

## Name

compile — compile a string with yabasic-code on the fly

## Synopsis

    compile(code$)

## Description

This is an advanced command (closely related with the `execute`-command). It allows you to compile a string of yabasic-code (which is the only argument). Afterwards the compiled code is a normal part of your program.

Note, that there is no way to remove the compiled code.

## Example

    compile("sub mysub(a):print a:end sub")
    mysub(2)

This example creates a function named `mysub`, which simply prints its single argument.

## See also

`execute`

## Name

continue — start the next iteration of a `for`-, `do`-, `repeat`- or `while`-loop

## Synopsis

    continue

## Description

You may use `continue` within any loop to start the next iteration immediately. Depending on the type of the loop, the loop-condition will or will not be checked. Especially: `for`- and `while`-loops will evaluate their respective conditions, `do`- and `repeat`-loops will not.

Remark: Another way to change the flow of execution within a loop, is the `break`-command.

## Example

    for a=1 to 100
      if mod(a,2)=0 continue
      print a
    next a

This example will print all odd numbers between 1 and 100.

## See also

`for`, `do`, `repeat`, `while`, `break`

## Name

cos() — return the cosine of its single argument

## Synopsis

    x=cos(angle)

## Description

The `cos`-function expects an angle (in radian) and returns its cosine.

## Example

    print cos(pi)

This example will print `-1`.

## See also

`acos`, `sin`

### D

## Name

data — introduces a list of data-items

## Synopsis

    data 9,"world"
    …
    read b,a$

## Description

The `data`-keyword introduces a list of comma-separated list of strings or numbers, which may be retrieved with the `read`-command.

The `data`-command itself does nothing; it just stores data. A single `data`-command may precede an arbitrarily long list of values, in which strings or numbers may be mixed at will.

yabasic internally uses a `data-pointer` to keep track of the current location within the `data`-list; this pointer may be reset with the `restore`-command.

## Example

    do
      restore
      for a=1 to 4
        read num$,num
        print num$,"=",num
      next a
    loop
    data "eleven",11,"twelve",12,"thirteen",13,"fourteen",14

This example just prints a series of lines `eleven=11` up to `fourteen=14` and so on without end.

The `restore`-command ensures that the list of `data`-items is read from the start with every iteration.

## See also

`read`, `restore`

## Name

date$ — returns a string with various components of the current date

## Synopsis

    a$=date$

## Description

The `date$`-function (which must be called without parentheses; i.e. `date$()` would be an error) returns a string containing various components of a date; an example would be `4-05-27-2004-Thu-May`. This string consists of various fields separated by hyphens ("`-`"):

- The day within the week as a number in the range 0 (=Sunday) to 6 (=Saturday) (in the example above: `4`, i.e. thursday).

- The month as a number in the range 1 (=January) to 12 (=December) (in the example: `5` which stands for May).

- The day within the month as a number in the range 1 to 31 (in the example: `27`).

- The full, 4-digit year (in the example: `2004`, which reminds me that I should adjust the clock within my computer …).

- The abbreviated name of the day within the week (`Mon` to `Sun`).

- The abbreviated name of the month (`Jan` to `Dec`).

Therefore the whole example above (`4-05-27-2004-Thu-May`) would read: day 4 in the week (counting from 0), May 27 in the year 2004, which is a Thursday in May.

Note, that all fields within the string returned by `date$` have a fixed with (numbers are padded with zeroes); therefore it is easy to extract the various fields of a date format with `mid$`.

## Example

    rem   Two ways to print the same ...

    print mid$(date$,3,10)

    dim fields$(6)
    a=split(date$,fields$(),"-")
    print fields$(2),"-",fields$(3),"-",fields$(4)

This example shows two different techniques to extract components from the value returned by `date$`. The `mid$`-function is the preferred way, but you could just as well `split` the return-value of `date$` at every "-" and store the result within an array of strings.

## See also

`time$`

## Name

dec() — convert a base 2 or base 16 number into decimal form

## Synopsis

    a=dec(number$)
    a=dec(number$,base)

## Description

The `dec`-function takes the string-representation of a base-2 or base-16 (which is the default) number and converts it into a decimal number. The optional second argument (`base`) might be used to specify a base other than 16. However, currently only base 2 or base 16 are supported.

## Example

    input "Please enter a binary number: " a$
    print a$," is ",dec(a$)

## See also

`bin$`, `hex$`

## Name

default — mark the default-branch within a `switch`-statement

## Synopsis

    switch a+3
    case 1
      …
    case 2
      …
    default
      …
    end switch

## Description

The `default`-clause is an optional part of the `switch`-statement (see there for more information). It introduces a series of statements, that should be executed, if none of the cases matches, that have been specified before (each with its own `case`-clause).

So `default` specifies a default to be executed, if none of the explicitly named cases matches; hence its name.

## Example

    print "Please enter a number between 0 and 6,"
    print "specifying a day in the week."
    input d
    switch d
    case 0:print "Monday":break
    case 1:print "Tuesday":break
    case 2:print "Wednesday":break
    case 3:print "Thursday":break
    case 4:print "Friday":break
    case 5:print "Saturday":break
    case 6:print "Sunday":break
    default:print "Hey you entered something invalid !"
    end switch

This program translates a number between 0 and 6 into the name of a weekday; the `default`-case is used to detect (and complain about) invalid input.

## See also

`sub`, `case`

## Name

dim — create an array prior to its first use

## Synopsis

    dim array(x,y)
    dim array$(x,y)

## Description

The `dim`-command prepares one or more arrays (of either strings or numbers) for later use. This command can also be used to enlarges an existing array.

When an array is created with the `dim`-statement, memory is allocated and all elements are initialized with either 0 (for numerical arrays) or "" (for string arrays).

If the array already existed, and the `dim`-statement specifies a larger size than the current size, the array is enlarged and any old content is preserved.

Note, that `dim` cannot be used to shrink an array: If you specify a size, that is smaller than the current size, the `dim`-command does nothing.

Finally: To create an array, that is only known within a single subroutine, you should use the command `local`, which creates local variables as well as local arrays.

## Example

    dim a(5,5)
    for x=1 to 5:for y=1 to 5
      a(x,y)=int(ran(100))
    next y:next x
    printmatrix(a())
    dim a(7,7)
    printmatrix(a())

    sub printmatrix(ar())
      local x,y,p,q
      x=arraysize(ar(),1)
      y=arraysize(ar(),2)
      for q=1 to y
        for p=1 to y
          print ar(p,q),"\t";
        next p
        print
      next q
    end sub

This example creates a 2-dimenional array (i.e. a matrix) with the `dim`-statement and fills it with random numbers. The second `dim`-statement enlarges the array, all new elements are filled with 0.

The subroutine `printmatrix` just does, what its name says.

## See also

`arraysize`, `arraydim`, `local`

## Name

do — start a (conditionless) `do-loop`

## Synopsis

    do
    …
    loop

## Description

Starts a loop, which is terminated by `loop`; everything between `do` and `loop` will be repeated forever. This loop has no condition, so it is an infinite loop; note however, that a `break`- or `goto`-statement might be used to leave this loop anytime.

## Example

    do
      a=a+1
      print a
      if (a>100) break
    loop

This example prints the numbers between 1 and 101. The `break`-statement is used to leave the loop.

## See also

`loop`, `repeat`, `while`, `break`

## Name

doc — special comment, which might be retrieved by the program itself

## Synopsis

    doc   This is a comment
    docu  This is another comment

## Description

Introduces a comment, which spans up to the end of the line. But other than the `rem`-comment, any `docu`-comment is collected within the special `docu$`-array and might be retrieved later on. Moreover you might invoke yabasic -docu foo.yab on the commandline to retrieve the embedded documentation within the program `foo.yab`.

Instead of `doc` you may just as well write `docu` or even `documentation`.

## Example

    rem   Hi, this has been written by me
    rem
    doc   This program asks for a number and
    doc   prints this number multiplied with 2
    rem
    rem   Print out rhe above message
    for a=1 to arraysize(docu$()):print docu$(a):next a

    rem   Read and print the number
    input "Please input a number: " x
    print x*2

This program uses the comments within its code to print out a help message for the user.

The contents of the `doc`-lines are retrieved from the `docu$`-array; if you do not want a comment to be collected within this array, use the `rem`-statement instead.

## See also

`docu$`, `rem`

## Name

docu$ — special array, containing the contents of all docu-statement within the program

## Synopsis

    a$=docu$(1)

## Description

Before your program is executed, yabasic collects the content of all the `doc`-statements within your program within this 1-dimensional array (well only those within the main-program, libraries are skipped).

You may use the `arraysize` function to find out, how many lines it contains.

## Example

    docu
    docu  This program reads two numbers
    docu  and adds them.
    docu

    rem retrieve and print the embedded documentation
    for a=1 to arraysize(docu$(),1)
      print docu$(a)
    next a

    input "First number: " b
    input "Second number: " c

    print "The sum of ",b," and ",c," is ",b+c

This program uses the embedded documentation to issue a usage-message.

## See also

`arraydim`, `rem`

## Name

dot — draw a dot in the graphic-window

## Synopsis

    dot x,y
    clear dot x,y

## Description

Draws a dot at the specified coordinates within your graphic-window. If printing is in effect, the dot appears on your printout too.

Use the functions `peek("winheight")` or `peek("winwidth")` to get the size of your window and hence the boundaries of the coordinates specified for the `dot`-command.

## Example

    open window 200,200
    circle 100,100,100
    do
      x=ran(200):y=ran(200)
      dot x,y
      total=total+1
      if (sqrt((x-100)^2+(y-100)^2)<100) in=in+1
      print 4*in/total
    loop

This program uses a well known algorithm to compute π.

## See also

`line`, `open window`

### E

## Name

else — mark an alternative within an `if`-statement

## Synopsis

    if (…) then
      …
    else
      …
    endif

## Description

The `else`-statement introduces the alternate branch of an `if`-statement. I.e. it starts the sequence of statements, which is executed, if the condition of the `if`-statement is not true.

## Example

    input "Please enter a number: " a
    if (mod(a,2)=1) then
      print a," is odd."
    else
      print a," is even."
    endif

This program detects, if the number you have entered is even or odd.

## See also

`if`

## Name

elsif — starts an alternate condition within an `if`-statement

## Synopsis

    if (…) then
      …
    elseif (…)
      …
    elsif (…) then
      …
    else
      …
    endif

## Description

The `elsif`-statement is used to select a single alternative among a series of choices.

With each `elsif`-statement you may specify a condition, which is tested, if the main condition (specified with the `if`-statement) has failed. Note that `elsif` might be just as well written as `elseif`.

Within the example below, two variables `a` and `b` are tested against a range of values. The variable `a` is tested with the `elsif`-statement. The very same tests are performed for the variable `b` too; but here an involved series of `if`-`else`-statements is employed, making the tests much more obscure.

## Example

    input "Please enter a number: " a
    if (a<0) then
      print "less than 0"
    elseif (a<=10) then
      print "between 0 and 10"
    elsif (a<=20)
      print "between 11 and 20"
    else
      print "over 20"
    endif

    input "Please enter another number: " b
    if (b<0) then
      print "less than 0"
    else
      if (b<=10) then
        print "between 0 and 10"
      else
        if (b<=20) then
          print "between 11 and 20"
        else
          print "over 20"
        endif
      endif
    endif

Note, that the very same tests are performed for the variables `a` and `b`, but can be stated much more clearly with the `elsif`-statement.

Note, that `elsif` might be written as `elseif` too, and that the keyword `then` is optional.

## See also

`if`, `else`

## Name

end — terminate your program

## Synopsis

    end

## Description

Terminate your program. Much (but not exactly) like the `exit` command.

Note, that `end` may not end your program immediately; if you have opened a window or called `clear screen`, yabasic assumes, that your user wants to study the output of your program after it has ended; therefore it issues the line `---Program done, press RETURN---` and waits for a key to be pressed. If you do not like this behaviour, consider using `exit`.

## Example

    print "Do you want to continue ?"
    input "Please answer y(es) or n(o): " a$
    if (lower$(left$(a$,1))="n") then
      print "bye"
      end
    fi

## See also

`exit`

## Name

endif — ends an `if`-statement

## Synopsis

    if (…) then
      …
    endif

## Description

The `endif`-statement closes (or ends) an `if`-statement.

Note, that `endif` may be written in a variety of other ways: `end if`, `end-if` or even `fi`.

The `endif`-statement must be omitted, if the `if`-statement does not contain the keyword `then` (see the example below). Such an `if`-statement without `endif` extends only over a single line.

## Example

    input "A number please: " a
    if (a<10) then
      print "Your number is less than 10."
    endif

    REM  and now without endif

    input "A number please: " a
    if (a<10) print "Your number is less than 10."

## See also

`if`

## Name

end sub — ends a subroutine definition

## Synopsis

    sub foo(…)
      …
    end sub

## Description

Marks the end of a subroutine-definition (which starts with the `sub`-keyword). The whole concept of subroutines is explained within the entry for `sub`.

## Example

    print foo(3)

    sub foo(a)
      return a*2
    end sub

This program prints out `6`. The subroutine `foo` simply returns twice its argument.

## See also

`sub`

## Name

eof — check, if an open file contains data

## Synopsis

    open 1,"foo.bar"
    if (eof(1)) then
       …
    end if

## Description

The `eof`-function checks, if there is still data left within an open file. As an argument it expects the file-number as returned by (or used within) the `open`-function (or statement).

## Example

    a=open("foo.bar")
    while(not eof(a))
      input #a,a$
      print a$
    end while

This example will print the contents of the file "foo.bar". The `eof`-function will terminate the loop, if there is no more data left within the file.

## See also

`open`

## Name

eor() — compute the bitwise exclusive or of its two arguments

## Synopsis

    print eor(a,b)

## Description

The `eor`-function takes two arguments and computes their bitwise exclusive or. See your favorite introductory text on informatics for an explanation of this function.

The `xor`-function is the same as the `eor` function; both are synonymous; however they have each their own description, so you may check out the entry of `xor` for a slightly different view.

## Example

    for a=0 to 3
      for b=0 to 3
        print fill$(bin$(a))," eor ",fill$(bin$(b))," = ",fill$(bin$(eor(a,b)))
      next b
    next a

    sub fill$(a$)
      return right$("0"+a$,2)
    end sub

This example prints a table, from which you may figure, how the `eor`-function is computed.

## See also

`and`, `or`

## Name

error — raise an error and terminate your program

## Synopsis

    error "Wrong, wrong, wrong !!"

## Description

Produces the same kind or error messages, that yabasic itself produces (e.g. in case of a syntax-error). The single argument is issued along with the current line-number.

## Example

    input "Please enter a number between 1 and 10: " a
    if (a<1 or a>10) error "Oh no ..."

This program is very harsh in checking the users input; instead of just asking again, the program terminates with an error, if the user enters something wrong.

The error message would look like this:

    ---Error in t.yab, line 2: Oh no ...
    ---Error: Program stopped due to an error

## See also

Well, there should be a corresponding called `warning`; unfortunately ther is none yet.

## Name

euler — another name for the constant `2.71828182864`

## Synopsis

    foo=euler

## Description

`euler` is the well known constant named after Leonard Euler; its value is `2.71828182864`. `euler` is not a function, so parens are not allowed (i.e. `euler()` will produce an error). Finally, you may not assign to `euler`; it wouldn't sense anyway, because it is a constant.

## Example

    print euler

## See also

`pi`

## Name

execute$() — execute a user defined subroutine, which must return a string

## Synopsis

    print execute$("foo$","arg1","arg2")

## Description

`execute$` can be used to execute a user defined subroutine, whose name may be specified as a string expression.

This feature is the only way to execute a subroutine, whose name is not known by the time you write your program. This might happen, if you want to execute a subroutine, which is compiled (using the `compile` command) during the course of execution of your program.

Note however, that the `execute$`-function is not the preferred method to execute a user defined subroutine; almost all cases you should just execute a subroutine by writing down its name within your yabasic program (see the example).

## Example

    print execute$("foo$","Hello","world !")
    sub foo$(a$,b$)
      return a$+" "+b$
    end sub

The example simply prints `Hello world !`, which is the return value of the user defined subroutine `foo$`. The same could be achieved by executing:

    print foo$(a$,b$)

## See also

`compile`, `execute`

## Name

execute() — execute a user defined subroutine, which must return a number

## Synopsis

    print execute("bar","arg1","arg2")

## Description

The `execute`-function is the counterpart of the `execute$`-function (please see there for some caveats). `execute` executes subroutines, which returns a number.

## Example

    print execute("bar",2,3)
    sub bar(a,b)
      return a+b
    end sub

## See also

`compile`, `execute$`

## Name

exit — terminate your program

## Synopsis

    exit
    exit 1

## Description

Terminate your program and return any given value to the operating system. `exit` is similar to `end`, but it will terminate your program immediately, no matter what.

## Example

    print "Do you want to continue ?"
    input "Please answer y(es) or n(o): " a$
    if (lower$(left$(a$,1))="n") exit 1

## See also

`end`

## Name

exp() — compute the exponential function of its single argument

## Synopsis

    foo=exp(bar)

## Description

This function computes e to the power of its argument, where e is the well known euler constant `2.71828182864`.

The `exp`-function is the inverse of the `log`-function.

## Example

    open window 100,100
    for x=0 to 100
       dot x,100-100*exp(x/100)/euler
    next x

This program plots part of the `exp`-function, however the range is rather small, so that you may not recognize the function from this plot.

## See also

`log`

## Name

export — mark a function as globally visible

## Synopsis

    export sub foo(bar)
    …
    end sub

## Description

The `export`-statement is used within libraries to mark a user defined subroutine as visible outside the library wherein it is defined. Subroutines, which are not exported, must be qualified with the name of the library, e.g. `foo.baz` (where `foo` is the name of the library and `baz` the name of the subroutine); exported subroutines may be used without specifying the name of the library, e.g. `bar`.

Therefore `export` may only be useful within libraries.

## Example

The library `foo.bar` (which is listed below) defines two functions `bar` and `baz`, however only the function `bar` is exported and therefore visible even outside the library; `baz` is not exported and may only be used within the library `foo.yab`:

    export sub bar()
      print "Hello"
    end sub

    sub baz()
      print "World"
    end sub

Now within your main program `cux.yab` (which `import`s the library foo.yab); note that this program produces an error:

    import foo

    print "Calling subroutine foo.bar (okay) ..."
    foo.bar()
    print "done."

    print "Calling subroutine bar (okay) ..."
    bar()
    print "done."

    print "Calling subroutine foo.baz (okay) ..."
    foo.baz()
    print "done."

    print "Calling subroutine baz (NOT okay) ..."
    baz()
    print "done."

The output when executing yabasic foo.yab is this:

    Calling subroutine foo.bar (okay) ...
    Hello
    done.
    Calling subroutine bar (okay) ...
    Hello
    done.
    Calling subroutine foo.baz (okay) ...
    World
    done.
    Calling subroutine baz (NOT okay) ...
    ---Error in main.yab, line 16: can't find subroutine 'baz'
    ---Dump: sub baz() called in main.yab,16
    ---Error: Program stopped due to an error

As the error message above shows, the subroutine `baz` must be qualified with the name of the library, if used outside the library, wherein it is defined (e.g. `foo.baz`. I.e. outside the library `foo.yab` you need to write `foo.baz`. `baz` alone would be an error.

The subroutine `bar` (without adding the name of the library) however may (and probably should) be used in any program, which imports the library `foo.yab`.

### Note

In some sense the set of exported subroutines constitutes the interface of a library.

## See also

`sub`, `import`

### F

## Name

false — a constant with the value of 0

## Synopsis

    okay=false

## Description

The constant `false` can be assigned to variables which later appear in conditions (e.g. within an `if`-statement.

`false` may also be written as `FALSE` or even `FaLsE`.

## Example

    input "Please enter a number between 1 and 10: " a
    if (check_input(a)) print "Okay"

    sub check_input(x)
      if (x>10 or x<1) return false
      return true
    end sub

The subroutine `check_input` checks its argument and returns `true` or `false` according to the outcome of the check..

## See also

`true`

## Name

fi — another name for `endif`

## Synopsis

    if (…)
    …
    fi

## Description

`fi` marks the end of an `if`-statement and is exactly equivalent to `endif`, please see there for further information.

## Example

    input "A number please: " a
    if (a<10) then
      print "Your number is less than 10."
    fi

## See also

`endif`

## Name

fill — draw a filled `circle`s, `rectangle`s or `triangle`s

## Synopsis

    fill rectangle 10,10,90,90
    fill circle 50,50,20
    fill triangle 10,20,20,10,20,20

## Description

The keyword `fill` may be used within the `circle`, `rectangle` or `triangle` command and causes these shapes to be filled.

`fill` can be used in conjunction with and wherever the `clear`-clause may appear. Used alone, `fill` will fill the interior of the shape (circle, rectangle or triangle); together with `clear` the whole shape (including its interior) is erased.

## Example

    open window 200,200
    fill circle 100,100,50
    clear fill rectangle 10,10,90,90

This opens a window and draws a pacman-like figure.

## See also

`clear`, `circle`, `rectangle`, `triangle`

## Name

for — starts a `for`-loop

## Synopsis

    for a=1 to 100 step 2
      …
    next a

## Description

The `for`-loop lets its numerical variable (`a` in the synopsis) assume all values within the given range. The optional `step`-clause may specify a value (default: 1) by which the variable will be incremented (or decremented, if `step` is negative).

Any `for`-statement can be replaced by a set of `if`s and `goto`s; as you may infer from the example below this is normally not feasible. However if you want to know in detail how the `for`-statement works, you should study this example, which presents a `for`-statement and an exactly equivalant series of `if`s and `goto`s.

## Example

    for a=1 to 10 step 2:print a:next

    a=1
    label check
    if (a>10) goto done
      print a
      a=a+2
    goto check
    label done

This example simply prints the numbers 1, 3, 5, 7 and 9. It does this twice: First with a simple `for`-statement and then with `if`s and `goto`s.

## See also

`step`, `next`

## Name

frac() — return the fractional part of its numeric argument

## Synopsis

    x=frac(y)

## Description

The `frac`-function takes its argument, removes all the digits to the left of the comma and just returns the digits right of the comma, i.e. the fractional part.

Refer to the example to learn how to rewrite `frac` by employing the `int`-function.

## Example

    for a=1 to 10
      print frac(sqr(a))
      print sqr(a)-int(sqr(a))
    next a

The example prints the fractional part of the square root of the numbers between 1 and 10. Each result is computed (and printed) twice: Once by employing the `frac`-function and once by employing the `int`-function.

## See also

`int`

### G

## Name

getbit$() — return a string representing the bit pattern of a rectangle within the graphic window

## Synopsis

    a$=getbit$(10,10,20,20)
    a$=getbit$(10,10 to 20,20)

## Description

The function `getbit` returns a string, which contains the encoded bit-pattern of a rectangle within graphic window; the four arguments represent the borders of the rectangle. The string returned might later be fed to the `putbit`-command.

The `getbit$`-function might be used for simple animations (as in the example below).

## Example

    open window 40,40
    fill circle 20,20,18
    circle$=getbit$(0,0,40,40)
    close window

    open window 200,200
    for x=1 to 200
      putbit circle$,x,80
    next x

This example features a circle moving from left to right over the window.

## See also

`putbit`

## Name

getscreen$() — returns a string representing a rectangular section of the text terminal

## Synopsis

    a$=getscreen$(2,2,20,20)

## Description

The `getscreen$` function returns a string representing the area of the screen as specified by its four arguments (which specify two corners). I.e. everything you have printed within this rectangle will be encoded in the string returned (including any colour-information).

Like most other commands dealing with advanced text output, `getscreen$` requires, that you have called `clear screen` before.

## Example

    clear screen

    for a=1 to 1000:
    	print color("red") "1";
    	print color("green") "2";
    	print color("blue") "3";
    next a
    screen$=getscreen$(10,10,40,10)
    print at(10,10) " Please Press 'y' or 'n' ! "
    a$=inkey$
    putscreen screen$,10,10

This program fills the screen with colored digits and afterwards asks the user for a choice (`Please press 'y' or 'n' !` ). Afterwards the area of the screen, which has been overwritten by the question will be restored with its previous contents, whhch had been saved via `getscreen$`.

## See also

`putscreen$`

## Name

glob() — check if a string matches a simple pattern

## Synopsis

    if (glob(string$,pattern$)) …

## Description

The `glob`-function takes two arguments, a string and a (glob-) pattern, and checks if the string matches the pattern. However `glob` does not employ the powerful rules of regular expressions; rather it has only two special characters: `*` (which matches any number (even zero) of characters) and `?` (which matches exactly a single character).

## Example

    for a=1 to 10
      read string$,pattern$
      if (glob(string$,pattern$)) then
        print string$," matches ",pattern$
      else
        print string$," does not match ",pattern$
      endif
    next a

    data "abc","a*"
    data "abc","a?"
    data "abc","a??"
    data "abc","*b*"
    data "abc","*"
    data "abc","???"
    data "abc","?"
    data "abc","*c"
    data "abc","A*"
    data "abc","????"

This program checks the string `abc` against various patterns and prints the result. The output is:

    abc matches a*
    abc does not match a?
    abc matches a??
    abc matches *b*
    abc matches *
    abc matches ???
    abc does not match ?
    abc matches *c
    abc does not match A*
    abc does not match ????

## See also

There are no related commands.

## Name

gosub — continue execution at another point within your program (and return later)

## Synopsis

    gosub foo

    …

    label foo
    …
    return

## Description

`gosub` remembers the current position within your program and then passes the flow of execution to another point (which is normally marked with a `label`). Later, when a `return`-statement is encountered, the execution is resumed at the previous location.

`gosub` is the traditional command for calling code, which needs to be executed from various places within your program. However, with subroutines yabasic offers a much more flexible way to achieve this (and more). Therefore `gosub` must to be considered obsolete.

## Example

    print "Do you want to exit ? "
    gosub ask
    if (r$="y") exit

    label ask
    input "Please answer yes or no, by typing 'y' or 'n': ",r$
    return

## See also

`return`, `goto`, `sub`, `label`, `on gosub`

## Name

goto — continue execution at another point within your program (and never come back)

## Synopsis

    goto foo

    …

    label foo

## Description

The `goto`-statement passes the flow of execution to another point within your program (which is normally marked with a `label`).

`goto` is normally considered obsolete and harmful, however in yabasic it may be put to the good use of leaving loops (e.g. `while` or `for`) prematurely. Note however, that subroutines may not be left with the `goto`-statement.

## Example

    print "Please press any key to continue."
    print "(program will continue by itself within 10 seconds)"
    for a=1 to 10
      if (inkey$(1)<>"") then goto done
    next a
    label done
    print "Hello World !"

Here the `goto`-statement is used to leave the `for`-loop prematurely.

## See also

`gosub`, `on goto`

### H

## Name

hex$() — convert a number into hexadecimal

## Synopsis

    print hex$(foo)

## Description

The `hex$`-function converts a number into a string with its hexadecimal representation. `hex$` is the inverse of the `dec`-function.

## Example

    open 1,"foo"
    while(!eof(1))
      print right$("0"+hex$(peek(1)),2)," ";
      i=i+1
      if (mod(i,10)=0) print
    end while
    print

This program reads the file `foo` and prints its output as a hex-dump using the `hex`-function.

## See also

`dec` `bin`

### I

## Name

if — evaluate a condition and execute statements or not, depending on the result

## Synopsis

    if (…) then
      …
    endif

    if (…) …

    if (…) then
      …
    else
      …
    endif

    if (…) then
      …
    elsif (…)
      …
    elsif (…) then
      …
    else
      …
    endif

## Description

The `if`-statement is used to evaluate a conditions and take actions accordingly. (As an aside, please note that there is no real difference between conditions and expressions.)

There are two major forms of the `if`-statement:

- The one-line-form without the keyword `then`:

      if (…) …

  This form evaluates the condition and if the result is `true` executes all commands (separated by colons) upt to the end of the line. There is neither an `endif` keyword nor an `else`-branch.

- The multi-line-form with the keyword `then`:

      if (…) then … elsif (…) … else … endif

  (where `elsif` and `else` are optional, whereas `endif` is not.

  According to the requirements of your program, you may specify:

  - `elsif(…)`, which specifies a condition, that will be evaluated only if the condition(s) whithin `if` or any preceding `elsif` did not match.

  - `else`, which introduces a sequence of commands, that will be executed, if none of the conditions above did match.

  - `endif` is required and ends the `if`-statement.

## Example

    input "Please enter a number between 1 and 4: " a
    if (a<=1 or a>=4) error "Wrong, wrong !"
    if (a=1) then
      print "one"
    elsif (a=2)
      print "two"
    elsif (a=3)
      print "three"
    else
      print "four"
    endif

The input-number between 1 and 4 is simply echoed as text (`one`, `two`, …). The example demonstrates both forms (short and long) of the `if`-statement (Note however, that the same thing can be done, probably somewhat more elegant, with the `switch`-statement).

## See also

`else`, `elsif`, `endif`, `conditions and expressions`.

## Name

import — import a library

## Synopsis

    import foo

## Description

The `import`-statement imports a library. It expects a single argument, which must be the name of a library (without the trailing `.yab`). This library will then be read and parsed and its subroutines (and variables) will be made available within the main program.

Libraries will first be searched within the current directory (i.e. the directory within which you have invoked yabasic), then within a special directory, whose exact location depends on your system. Typical values would be `/usr/lib` under Unix or `C:\yabasic\lib` under Windows. However only `yabasic -help-usage` may tell the truth. The location of this second directory may be changed with the option `-library` (either under Windows or Unix).

## Example

Lets say you have a yabasic-program `foo.yab`, which imports a library `lib.yab`. `foo.yab` reads:

    import lib

    rem  This works ...
    lib.x(0)

    rem  This works too ..
    x(1)

    rem  And this.
    lib.y(2)

    rem  But this not !
    y(3)

Now the library `lib.yab` reads:

    rem  Make the subroutine x easily available outside this library
    export sub x(a)
      print a
      return
    end sub

    rem  sub y must be referenced by its full name
    rem  outside this library
    sub y(a)
      print a
      return
    end sub

This program produces an error:

    0
    1
    2
    ---Error in foo.yab, line 13: can't find subroutine 'y'
    ---Dump: sub y() called in foo.yab,13
    ---Error: Program stopped due to an error

As you may see from the error message, yabasic is unable to find the subroutine `y` without specifying the name of the library (i.e. `lib.y`). The reason for this is, that `y`, other than `x`, is not exported from the library `lib.yab` (using the `export`-statement).

## See also

`export`, `sub`

## Name

inkey$ — wait, until a key is pressed

## Synopsis

    clear screen
    foo$=inkey$
    inkey$
    foo$=inkey$(bar)
    inkey$(bar)

## Description

The `inkeys$`-function waits, until the user presses a key on the keyboard or a button of his mouse, and returns this very key. An optional argument specifies the number of seconds to wait; if omitted, `inkey$` will wait indefinitely.

`inkey$` may only be used, if `clear screen` has been called at least once.

For normal keys, yabasic simply returns the key, e.g. `a`, `1` or `!`. For function keys you will get `f1`, `f2` and so on. Other special keys will return these strings respectively: `enter`, `backspace`, `del`, `esc`, `scrnup` (for screen up), `scrndown` and `tab`. Modifier keys (e.g. `ctrl`, `alt` or `shift`) by themselves can not be detected (however, if you press `shift` and e.g. `a` simultaniously, `inkey$` will return the letter `A` instead of `a` of course).

If a graphical window has been opened (via `open window`) any mouseclick within this window will be returned by `inkey$` too. The string returned (e.g. `MB1d+0:0028,0061`, `MB2u+0:0028,0061` or `MB1d+1:0028,0061`) is constructed as follows:

- Every string associated with a mouseclick will start with the fixed string `MB`

- The next digit (`1`, `2` or `3`) specifies the mousebutton pressed.

- A single letter, `d` or `u`, specifies, if the mousebutton has been pressed or released: `d` stands for down, i.e. the mousebutton has been pressed; `u` means up, i.e. the mousebutton has been released.

- The plus-sign ('`+`'), which follows is always fixed.

- The next digit (in the range 0 to 7) encodes the modifier keys pressed, where `1` stands for `shift`, `2` stands for `alt` and `4` stands for `ctrl`.

- The next four digits (e.g. `0028`) contain the x-position, where the mousebutton has been pressed.

- The comma to follow is always fixed.

- The last four digits (e.g. `0061`) contain the y-position, where the mousebutton has been pressed.

All those fields are of fixed length, so you may use functions like `mid$` to extract certain fields. However, note that with `mousex`, `mousey`, `mouseb` and `mousemod` there are specialized functions to return detailed information about the mouseclick. Finally it should be noted, that `inkey$` will only register mouseclicks within the graphic-window; mouseclicks in the text-window cannot be detected.

`inkey$` accepts an optional argument, specifying a timeout in seconds; if no key has been pressed within this span of time, an empty string is returned. If the timeout-argument is omitted, `inkey$` will wait for ever.

## Example

    clear screen
    open window 100,100
    print "Press any key or press 'q' to stop."
    repeat
      a$=inkey$
      print a$
    until(a$="q")

This program simply returns the key pressed. You may use it, to learn, which strings are returned for the special keys on your keyboard (e.g. function-keys).

## See also

`clear screen`,`mousex`, `mousey`, `mouseb`, `mousemod`

## Name

input — read input from the user (or from a file) and assign it to a variable

## Synopsis

    input a
    input a,b,c
    input a$
    input "Hello" a
    input #1 a$

## Description

`input` reads the new contents of one or many (numeric- or string-) variables, either from the keyboard (i.e. from you) or from a file. An optional first string-argument specifies a prompt, which will be issued before reading any contents.

If you want to read from an open file, you need to specify a hash ('#'), followed by the number, under which the file has been opened.

Note, that the input is split at spaces, i.e. if you enter a whole line consisting of many space-separated word, the first `input`-statement will only return the first word; the other words will only be returned on subsequent calls to `input`; the same applies, if a single `input` reads multiple variables: The first variable gets only the first word, the second one the second word, and so on. If you don't like this behaviour, you may use `line input`, which returns a whole line (including embedded spaces) at once.

## Example

    input "Please enter the name of a file to read: " a$
    open 1,a$
    while(!eof(1))
      input #1 b$
      print b$
    wend

If this program is stored within a file `test.yab` and you enter this name when prompted for a file to read, you will see this output:

    Please enter the name of a file to read: t.yab
    input
    "Please
    enter
    the
    name
    of
    a
    file
    to
    read:
    "
    a$
    open
    1,a$
    while(!eof(1))
    input
    #1
    b$
    print
    b$
    wend

## See also

`line input`

## Name

instr() — searches its second argument within the first; returns its position if found

## Synopsis

    print instr(a$,b$)
    if (instr(a$,b$)) …
    pos=instr(a$,b$,x)

## Description

The `instr`-functions requires two string arguments and searches the second argument within the first. If the second argument can be found within the first, the position is returned (counting from one). If it can not be found, the `instr`-function returns 0; this makes this function usable within the condition of an `if`-statement (see the example below).

If you supply a third, numeric argument to the `instr`-function, it will be used as a starting point for the search. Therefore `instr("abcdeabcdeabcde","e",8)` will return 10, because the search for an "`e`" starts at position 8 and finds the "`e`" at position 10 (and not the one at position 5).

## Example

    input "Please enter a text containing the string 'bumf': " a$
    if (instr(a$,"bumf")) then
      print "Well done !"
    else
      print "not so well ..."
    endif

## See also

`rinstr`

## Name

int() — return the integer part of its single numeric argument

## Synopsis

    print int(a)

## Description

The `int`-function returns only the digits before the comma; `int(2.5)` returns `2` and `int(-2.3)` returns `-2`.

## Example

    input "Please enter a whole number between 1 and 10: " a
    if (a=int(a) and a>=1 and a<=10) then
      print "Thanx !"
    else
      print "Never mind ..."
    endif

## See also

`frac`

### L

## Name

label — mark a specific location within your program for `goto`, `gosub` or `restore`

## Synopsis

    label foo

    …

    goto foo

## Description

The `label`-command can be used to give a name to a specific location within your program. Such a position might be referred from one of three commands: `goto`, `gosub` and `restore`.

You may use labels safely within libraries, because a label (e.g. `foo`) does not collide with a label with the same name within the main program or within another library; yabasic will not mix them up.

As an aside, please note, that line numbers are a special (however deprecated) case of labels; see the second example below.

## Example

    for a=1 to 100
      if (rand(10)>5) goto done
    next a
    label done

    10 for a=1 to 100
    20   if (rand(10)>5) goto 40
    30 next a
    40

Within this example, the `for`-loop will probably be left prematurely with a `goto`-statement. This task is done twice: First with labels and then again with line numbers.

## See also

`gosub`, `goto`.

## Name

left$() — return (or change) left end of a string

## Synopsis

    print left$(a$,2)
    left$(b$,3)="foobar"

## Description

The `left$`-function accepts two arguments (a string and a number) and returns the part from the left end of the string, whose length is specified by its second argument. Loosely spoken, it simply returns the requested number of chars from the left end of the given string.

Note, that the `left$`-function can be assigned to, i.e. it may appear on the left hand side of an assignment. In this way it is possible to change a part of the variable used within the `left$`-function. Note, that that way the length of the string cannot be changed, i.e. characters might be overwritten, but not added. For an example see below.

## Example

    input "Please answer yes or no: " a$
    l=len(a$):a$=lower$(a$):print "Your answer is ";
    if (left$("yes",l)=a$ and l>=1) then
      print "yes"
    elsif (left$("no",l)=a$ and l>=1) then
      print "no"
    else
      print "?"
    endif

This example asks a simple yes/no question and goes some way to accept even incomplete input, while still being able to reject invalid input.

This second example demonstrates the capability to assign to the `left$`-function.

    a$="Heiho World !"
    print a$
    left$(a$,5)="Hello"
    print a$

## See also

`right$`, `mid$`

## Name

len() — return the length of a string

## Synopsis

    x=len(a$)

## Description

The `len`-function returns the length of its single string argument.

## Example

    input "Please enter a password: " a$
    if (len(a$)<6) error "Password too short !"

This example checks the length of the password, that the user has entered.

## See also

`left$`, `right$` and `mid$`,

## Name

line — draw a line

## Synopsis

    open window 100,100
    line 0,0,100,100
    line 0,0 to 100,100
    new curve
    line 100,100
    line to 100,100

    open window 100,100
    clear line 0,0,100,100
    clear line 0,0 to 100,100
    new curve
    clear line 100,100
    clear line to 100,100

## Description

The `line`-command draws a line. Simple as this is, the `line`-command has a large variety of forms as they are listed in the synopsis above. Lets look at them a little closer:

- A line has a starting and an end point; therefore the `line`-command (normally) needs four numbers as arguments, representing these two points. This is the first form appearing within the synopsis.

- You may separate the two points with either '`,`' or `to`, which accounts for the second form of the `line`-command.

- The `line`-command may be used to draw a connected sequence of lines with a sequence of commands like `line x,y`; Each command will draw a line from the point where the last `line`-command left off, to the point specified in the arguments. Note, that you need to use the command `new curve` before you may issue such a `line`-command. See the example below.

- You may insert the word `to` for beauty: `line to x,y`, which does exactly the same as `line x,y`

- Finally, you may choose not to draw, but to erase the lines; this can be done by prepending the phrase `clear`. This account for all the other forms of the `line`-command.

## Example

    open window 200,200
    line 10,10 to 10,190
    line 10,190 to 190,190
    new curve
    for a=0 to 360
      line to 10+a*180/360,100+60*sin(a*pi/180)
    next a

This example draws a sine-curve (with an offset in x- and y-direction). Note, that the first `line`-command after `new curve` does not draw anything. Only the coordinates will be stored. The second iteration of the loop then uses these coordinates as a starting point for the first line.

## See also

`new curve`, `close curve`, `open window`

## Name

line input — read in a whole line of text and assign it to a variable

## Synopsis

    line input a
    line input a$
    line input "Hello" a
    line input #1 a$

## Description

In most respects `line input` is like the `input`-command: It reads the new contents of a variable, either from keyboard or from a file. However, `line input` always reads a complete line and assigns it to its variable. `line input` does not stop reading at spaces and is therefore the best way to read in a string which might contain whitespace. Note, that the final newline is stripped of.

## Example

    line input "Please enter your name (e.g. Frodo Beutelin): " a$
    print "Hello ",a$

Note that the usage of `line input` is essential in this example; a simple `input`-statement would only return the string up to the first space, e.g. `Frodo`.

## See also

`input`

## Name

local — mark a variable as local to a subroutine

## Synopsis

    sub foo()

      local a,b,c$,d(10),e$(5,5)

      …

    end sub

## Description

The `local`-command can (and should be) used to mark a variable (or array) as local to the containing subroutine. This means, that a local variable in your subroutine is totally different from a variable with the same name within your main program. Variables which are known everywhere within your program are called global in contrast.

Declaring variables within the subroutine as local helps to avoid hard to find bugs; therefore local variables should be used whenever possible.

Note, that the parameters of your subroutines are always local.

As you may see from the example, local arrays may be created without using the keyword `dim` (which is required only for global arrays).

## Example

    a=1
    b=1
    print a,b
    foo()
    print a,b

    sub foo()
      local a
      a=2
      b=2
    end sub

This example demonstrates the difference between `local` and global variables; it produces this output:

    1 1
    1 2

As you may see, the content of the global variable `a` is unchanged after the subroutine `foo`; this is because the assignment `a=2` within the subroutine affects the local variable `a` only and not the global one. However, the variable `b` is never declared local and therefore the subroutine changes the global variable, which is reflected in the output of the second print-statement.

## See also

`sub`, `static`, `dim`

## Name

log() — compute the natural logarithm

## Synopsis

    a=log(x)
    a=log(x,base)

## Description

The `log`-function computes the logarithm of its first argument. The optional second argument gives the base for the logarithm; if this second argument is omitted, the euler-constant 2.71828… will be taken as the base.

## Example

    open window 200,200
    for x=10 to 190 step 10:for y=10 to 190 step 10
      r=3*log(1+x,1+y)
      if (r>10) r=10
      if (r<1) r=1
      fill circle x,y,r
    next y:next x

This draws another nice plot.

## See also

`exp`

## Name

loop — marks the end of an infinite loop

## Synopsis

    do
      …
    loop

## Description

The `loop`-command marks the ends of a loop (which is started by `do`), wherein all statements within the loop are repeated forever. In this respect the `do loop`-loop is infinite, however, you may leave it anytime via `break` or `goto`.

## Example

    print "Hello, I will throw dice, until I get a 2 ..."
    do
      r=int(rand(6))+1
      print r
      if (r=2) break
    loop

## See also

`do`, `for`, `repeat`, `while`, `break`

## Name

lower$() — convert a string to lower case

## Synopsis

    l$=lower$(a$)

## Description

The `lower$`-function accepts a single string-argument and converts it to all lower case.

## Example

    input "Please enter a password: " a$
    if (a$=lower$(a$)) error "Your password is NOT mixed case !"

This example prompts for a password and checks, if it is really lower case.

## See also

`upper$`

## Name

ltrim$() — trim spaces at the left end of a string

## Synopsis

    a$=ltrim$(b$)

## Description

The `ltrim$`-function removes all whitespace from the left end of a string and returns the result.

## Example

    input "Please answer 'yes' or 'no' : " a$
    a$=lower$(ltrim$(rtrim$(a$)))
    if (len(a$)>0 and a$=left$("yes",len(a$))) then
      print "Yes ..."
    else
      print "No ..."
    endif

This example prompts for an answer and removes any spaces, which might precede the input; therefore it is even prepared for the (albeit somewhat pathological case, that the user first hits space before entering his answer.

## See also

`rtrim$`, `trim$`

### M

## Name

max() — return the larger of its two arguments

## Synopsis

    print max(a,b)

## Description

Return the maximum of its two arguments.

## Example

    dim m(10)
    for a=1 to 1000
      m=0
      For b=1 to 10
        m=max(m,ran(10))
      next b
      m(m)=m(m)+1
    next a

    for a=1 to 9
      print a,": ",m(a)
    next a

Within the inner `for`-loop (the one with the loop-variable `b`), the example computes the maximum of 10 random numbers. The outer loop (with the loop variable `a`) now repeats this process 1000 times and counts, how often each maximum appears. The last loop finally reports the result.

Now, the interesting question would be, which will be approached, when we increase the number of iterations from thousand to infinity. Well, maybe someone could just tell me `:-)`

## See also

`min`

## Name

mid$() — return (or change) characters from within a string

## Synopsis

    print mid$(a$,2,1)
    print mid$(a$,2)
    mid$(a$,5,3)="foo"
    mid$(a$,5)="foo"

## Description

The `mid$`-function requires three arguments: a string and two numbers, where the first number specifies a position within the string and the second one gives the number of characters to be returned; if you omit the second argument, the `mid$`-function returns all characters up to the end of the string.

Note, that you may assign to the `mid$`-function, i.e. `mid$` may appear on the left hand side of an assignment. In this way it is possible to change a part of the variable used within the `mid$`-function. Note, that that way the length of the string cannot be changed, i.e. characters might be overwritten, but not added. For an example see below.

## Example

    input "Please enter a string: " a$
    for a=1 to len(a$)
      if (instr("aeiou",lower$(mid$(a$,a,1)))) mid$(a$,a,1)="e"
    next a
    print "When you turn everything to lower case and"
    print "replace every vowel with 'e', your input reads:"
    print
    print a$

This example transforms the input string a bit, using the `mid$`-function to retrieve a character from within the string as well as to change it.

## See also

`left$` and `right$`.

## Name

min() — return the smaller of its two arguments

## Synopsis

    print min(a,b)

## Description

Return the minimum of its two argument.

## Example

    dim m(10)
    for a=1 to 1000
      m=min(ran(10),ran(10))
      m(m)=m(m)+1
    next a

    for a=1 to 9
      print a,": ",m(a)
    next a

For each iteration of the loop, the lower of two random number is recorded. The result is printed at the end.

## See also

`max`

## Name

mod() — compute the remainder of a division

## Synopsis

    print mod(a,b)

## Description

The `mod`-function divides its two arguments and computes the remainder. Note, that `a/b-int(a/b)` and `mod(a,b)` are always equal.

## Example

    clear screen
    print at(10,10) "Please wait ";
    p$="-\|/"
    for a=1 to 100
      rem  ... do something lengthy here, or simply sleep :-)
      pause(1)
      print at(22,10) mid$(p$,1+mod(a,4))
    next a

This example executes some time consuming action within a loop (in fact, it simply sleeps) and gives the user some indication of progress by displaying a turning bar (thats where the `mod()`-function comes into play).

## See also

`int`, `frac`

## Name

mouseb — extract the state of the mousebuttons from a string returned by `inkey$`

## Synopsis

    inkey$
    print mouseb()
    print mouseb
    a$=inkey$
    print mouseb(a$)

## Description

The `mouseb`-function is a helper function for decoding part of the (rather complicated) strings, which are returned by the `inkey$`-function. If a mousebutton has been pressed, the `mouseb`-function returns the number (1,2 or 3) of the mousebutton, when it is pressed and returns its negative (-1,-2 or -3), when it is released.

The `mouseb`-function accepts zero or one arguments. A single argument should be a string returned by the `inkey$`-function; if `mouseb` is called without any arguments, it returns the values from the last call to `inkey$`, which are stored implicitly and internally by yabasic.

### Note

Note however, that the value returned by the `mouseb`-function does not reflect the current state of the mousebuttons. It rather extracts the information from the string passed as an argument (or from the last call to the `inkey$`-function, if no argument is passed). So the value returned by `mouseb` reflects the state of the mousebuttons at the time the `inkey$`-function has been called; as opposed to the time the `mouseb`-function is called.

## Example

    open window 200,200
    clear screen
    print "Please draw lines; press (and keep it pressed)"
    print "the left mousebutton for the starting point,"
    print "release it for the end-point."
    do
      if (mouseb(release$)=1) press$=release$
      release$=inkey$
      if (mouseb(release$)=-1) then
        line mousex(press$),mousey(press$) to mousex(release$),mousey(release$)
      endif
    loop

This is a maybe the most simplistic line-drawing program possible, catching presses as well as releases of the first mousebutton.

## See also

`inkey$`, `mousex`, `mousey` and `mousemod`

## Name

mousemod — return the state of the modifier keys during a mouseclick

## Synopsis

    inkey$
    print mousemod()
    print mousemod
    a$=inkey$
    print mousemod(a$)

## Description

The `mousemod`-function is a helper function for decoding part of the (rather complicated) strings, which are returned by the `inkey$`-function if a mousebutton has been pressed. It returns the state of the keyboard modifiers (`shift`, `ctrl` or `alt`): If the `shift`-key is pressed, `mousemod` returns 1, for the `alt`-key 2 and for the `ctrl`-key 4. If more than one key is pressed, the sum of these values is returned, e.g. `mousemod` returns 5, if `shift` and `ctrl` are pressed simultaneously.

The `mousemod`-function accepts zero or one arguments. A single argument should be a string returned by the `inkey$`-function; if `mousemod` is called without any arguments, it returns the values from the last call to `inkey$` (which are stored implicitly and internally by yabasic).

### Note

Please see also the Note within the `mouseb`-function.

## Example

    open window 200,200
    clear screen
    do
      a$=inkey$
      if (left$(a$,2)="MB") then
        x=mousex(a$)
        y=mousey(a$)
        if (mousemod(a$)=0) then
          circle x,y,20
        else
          fill circle x,y,20
        endif
      endif
    loop

This program draws a circle, whenever a mousebutton is pressed; the circles are filled, when any modifier is pressed, and empty if not.

## See also

`inkey$`, `mousex`, `mousey` and `mouseb`

## Name

mousex — return the x-position of a mouseclick

## Synopsis

    inkey$
    print mousex()
    print mousex
    a$=inkey$
    print mousex(a$)

## Description

The `mousex`-function is a helper function for decoding part of the (rather complicated) strings, which are returned by the `inkey$`-function; It returns the x-position of the mouse as encoded within its argument.

The `mousex`-function accepts zero or one arguments. A single argument should be a string returned by the `inkey$`-function; if `mousex` is called without any arguments, it returns the values from the last call to `inkey$` (which are stored implicitly and internally by yabasic).

### Note

Please see also the Note within the `mouseb`-function.

## Example

    open window 200,200
    clear screen
    do
      a$=inkey$
      if (left$(a$,2)="MB") then
        line mousex,0 to mousex,200
      endif
    loop

This example draws vertical lines at the position, where the mousebutton has been pressed.

## See also

`inkey$`, `mousemod`, `mousey` and `mouseb`

## Name

mousey — return the y-position of a mouseclick

## Synopsis

    inkey$
    print mousey()
    print mousey
    a$=inkey$
    print mousey(a$)

## Description

The `mousey`-function is a helper function for decoding part of the (rather complicated) strings, which are returned by the `inkey$`-function. `mousey` returns the y-position of the mouse as encoded within its argument.

The `mousey`-function accepts zero or one arguments. A single argument should be a string returned by the `inkey$`-function; if `mousey` is called without any arguments, it returns the values from the last call to `inkey$` (which are stored implicitly and internally by yabasic).

### Note

Please see also the Note within the `mouseb`-function.

## Example

    open window 200,200
    clear screen
    do
      a$=inkey$
      if (left$(a$,2)="MB") then
        line 0,mousey to 200,mousey
      endif
    loop

This example draws horizontal lines at the position, where the mousebutton has been pressed.

## See also

`inkey$`, `mousemod`, `mousex` and `mouseb`

### N

## Name

new curve — start a new curve, that will be drawn with the `line`-command

## Synopsis

    new curve
    line to x,y

## Description

The `new curve`-function starts a new sequence of lines, that will be drawn by repeated `line to`-commands.

## Example

    open window 200,200
    ellipse(100,50,30,60)
    ellipse(150,100,60,30)
    sub ellipse(x,y,xr,yr)
      new curve
      for a=0 to 2*pi step 0.2
        line to x+xr*cos(a),y+yr*sin(a)
      next a
      close curve
    end sub

This example defines a subroutine `ellipse` that draws an ellipse. Within this subroutine, the ellipse is drawn as a sequence of lines started with the `new curve` command and closed with `close curve`.

## See also

`line`, `close curve`

## Name

next — mark the end of a for loop

## Synopsis

    for a=1 to 10
    next a

## Description

The `next`-keyword marks the end of a `for`-loop. All statements up to the `next`-keyword will be repeated as specified with the `for`-clause. Note, that the name of the variable is optional; so instead of `next a` you may write `next`.

## Example

    for a=1 to 300000
      for b=1 to 21+20*sin(pi*a/20)
        print "*";
      next b
      print
      sleep 0.1
    next a

This example simply plots a sine-curve until you fall asleep.

## See also

`for`

## Name

not — negate an expression; can be written as `!`

## Synopsis

    if (not a<b) then …
    bad=!okay

## Description

The keyword `not` (or `!` for short) is mostly used within conditions (e.g. within `if`- or `while`-statements). There it is employed to negate the condition or expression (i.e. turn `TRUE` into `FALSE` and vice versa)

However `not` can be used within arithmetic calculations too., simply because there is no difference between arithmetic and logical expressions.

## Example

    input "Please enter three ascending numbers: " a,b,c
    if (not (a<b and b<c)) error " the numbers you have entered are not ascending ..."

## See also

`and`,`or`

## Name

numparams — return the number of parameters, that have been passed to a subroutine

## Synopsis

    sub foo(a,b,c)
      if (numparams=1) …
      …
    end sub

## Description

Within a subroutine the local variable `numparam` or `numparams` contains the number of parameters, that have been passed to the subroutine. This information can be useful, because the subroutine may have been called with fewer parameters than actually declared. The number of values that actually have been passed while calling the subroutine, can be found in `numparams`.

Note, that arguments which are used in the definition of a subroutine but are left out during a call to it (thereby reducing the value of `numparams`) receive a value of `0` or `""` (empty string) respectively.

## Example

    a$="123456789"
    print part$(a$,4)
    print part$(a$,3,7)

    sub part$(a$,f,t)
      if (numparams=2) then
        return mid$(a$,f)
      else
        return mid$(a$,f,t-f+1)
      end if
    end sub

When you run this example, it will print `456789` and `34567`. Take a look at the subroutine `part$`, which returns part of the string which has been passed as an argument. If (besides the string) two numbers are passed, they define the starting and end position of the substring, that will be returned. However, if only one number is passed, the rest of the string, starting from this position will be returned. Each of these cases is recognized with the help of the `numparams` variable.

## See also

`sub`

### O

## Name

on goto — jump to one of multiple `gosub`-targets

## Synopsis

    on a gosub foo,bar,baz
      …
    label foo
      …
    return

    label bar
      …
    return

    label baz
      …
    return

## Description

The `on gosub` statement uses its numeric argument (the one between `on` and `gosub`) to select an element from the list of labels, which follows after the `gosub`-keyword: If the number is 1, the program does a `gosub` to the first label; if the number is 2, to the second and, so on. if the number is zero or less, the program continues at the position of the first label; if the number is larger than the total count of labels, the execution continues at the position of the last label; i.e. the first and last label in the list constitute some kind of fallback-slot.

Note, that the `on gosub`-command can no longer be considered state of the art; people (not me !) may even start to mock you, if you use it.

## Example

    do
      print "Please enter a number between 1 and 3: "
      print
      input "Your choice " a
      on a gosub bad,one,two,three,bad
    loop

    label bad
      print "No. Please between 1 and 3"
    return

    label one
      print "one"
    return

    label two
      print "two"
    return

    label three
      print "three"
    return

Note, how invalid input (a number less than 1, or larger than 3) is automatically detected.

## See also

`goto`, `on gosub/function>`

## Name

on goto — jump to one of many `goto`-targets

## Synopsis

    on a goto foo,bar,baz
      …
    label foo
      …
    label bar
      …
    label baz
      …

## Description

The `on goto` statement uses its numeric argument (the one between `on` and `goto` to select an element from the list of labels, which follows after the `goto`-keyword: If the number is 1, the execution continues at the first label; if the number is 2, at the second, and so on. if the number is zero or less, the program continues at the position of the first label; if the number is larger than the total count of labels, the execution continues at the position of the last label; i.e. the first and last label in the list constitute some kind of fallback-slot.

Note, that (unlike the `goto`-command) the `on goto`-command can no longer be considered state of the art; people may (not me !) even start to mock you, if you use it.

## Example

    label over
    print "Please Select one of these choices: "
    print
    print "  1 -- show time"
    print "  2 -- show date"
    print "  3 -- exit"
    print
    input "Your choice " a
    on a goto over,show_time,show_date,terminate,over

    label show_time
      print time$()
    goto over

    label show_date
      print date$()
    goto over

    label terminate
    exit

Note, how invalid input (a number less than 1, or larger than 3) is automatically detected; in such a case the question is simply issued again.

## See also

`goto`, `on gosub/function>`

## Name

on interrupt — change reaction on keyboard interrupts

## Synopsis

    on interrupt break
    …
    on interrupt continue

## Description

With the `on interrupt`-command you may change the way, how yabasic reacts on a keyboard interrupt; it comes in two variants: `on interrupt break` and `on interrupt continue`. A keyboard interrupt is produced, if you press `ctrl-C` on your keyboard; normally (and certainly after you have called `on interrupt break`), yabasic will terminate with an error message. However after the command `on interrupt continue` yabasic ignores any keyboard interrupt. This may be useful, if you do not want your program being interruptible during certain critical operations (e.g. updating of files).

## Example

    print "Please stand by while writing a file with random data ..."
    on interrupt continue
    open "random.data" for writing as #1
    for a=1 to 100
      print #1 ran(100)
      print a," percent done."
      sleep 1
    next a
    close #1
    on interrupt continue

This program writes a file with 100 random numbers. The `on interrupt continue` command insures, that the program will not be terminated on a keyboard interrupt and the file will be written entirely in any case. The `sleep`-command just stretches the process artificially to give you a chance to try a `ctrl-C`.

## See also

There is no related command.

## Name

open — open a file

## Synopsis

    open a,"file","r"
    open #a,"file","w"
    open #a,printer
    open "file" for reading as a
    open "file" for writing as #a
    a=open("file")
    a=open("file","r")
    if (open(a,"file")) …
    if (open(a,"file","w")) …

## Description

The `open`-command opens a file for reading or writing or a printer for printing text. `open` comes in a wide variety of ways; it requires these arguments:

filenumber

  In the synopsis this is `a` or `#a`. In yabasic each file is associated with a number between 1 and a maximum value, which depends on the operating system. For historical reasons the filenumber can be preceded by a hash ('`#`'). Note, that specifying a filenumber is optional; if it is omitted, the `open`-function will return a filenumber, which should then be stored in a variable for later reference. This filenumber can be a simple number or an arbitrary complex arithmetic expression, in which case braces might be necessary to save yabasic from getting confused.

filename

  In the synopsis above this is `"file"`. This string specifies the name of the file to open (note the important caveat on specifying these filenames).

accessmode

  In the synopsis this is `"r"`, `"w"`, `for reading` or `for writing`. This string or clause specifies the mode in which the file is opened; it may be one of:

  "r"

    Open the file for reading (may also be written as `for reading`). If the file does not exist, the command will fail. This mode is the default, i.e. if no mode is specified with the `open`-command, the file will be opened with this mode.

  "w"

    Open the file for writing (may also be written as `for writing`). If the file does not exist, it will be created.

  "a"

    Open the file for appending, i.e. what you write to the file will be appended after its initial contents. If the file does not exist, it will be created.

  "b"

    This letter may not appear alone, but may be combined with the other letters (e.g. `"rb"`) to open a file in binary mode (as opposed to text mode).

As you may see from the synopsis, the `open`-command may either be called as a command (without braces) or as a function (with braces). If called as a function, it will return the filenumber or zero if the operation fails. Therefore the `open`-function may be used within the condition of an `if`-statement.

If the `open`-command fails, you may use `peek("error")` to retrieve the exact nature of the error.

Furthermore note, that there is another, somewhat separate usage of the `open`-command; if you specify the bareword `printer` instead of a filename, the command opens a printer for printing text. Every text (and only text) you print to this file will appear on your printer. Note, that this is very different from printing graphics, as can be done with `open printer`.

Finally you may read the description for `peek("error")` to learn which errors may have happened during an `open`-call.

## Example

    open "foo.bar" for writing as #1
    print #1 "Hallo !"
    close #1
    if (not open(1,"foo.bar")) error "Could not open 'foo.bar' for reading"
    while(not eof(1))
      line input #1 a$
      print a$
    wend

This example simply opens the file `foo.bar`, writes a single line, reopens it and reads its contents again.

## See also

`close`, `print`, `peek`, `peek("error")` and `open printer`

## Name

open printer — open printer for printing graphics

## Synopsis

    open printer
    open printer "file"

## Description

The `open printer`-command opens a printer for printing graphics. The command requires, that a graphic window has been opened before. Everything that is drawn into this window will then be sent to the printer too.

A new piece of paper may be started with the `clear window`-command; the final (or only) page will appear after the `close printer`-command.

Note, that you may specify a filename with `open printer`; in that case the printout will be sent to a filename instead to a printer. Your program or the user will be responsible for sending this file to the printer afterwards.

If you use yabasic under Unix, you will need a postscript printer (because yabasic produces postscript output). Alternatively you may use ghostscript to transform the postscript file into a form suitable for your printer; but that is beyond the responsibility of yabasic.

## Example

    open window 200,200
    open printer
    line 0,0 to 200,200
    text 100,100,"Hallo"
    close window
    close printer

This example will open a window, draw a line and print some text within; everything will appear on your printer too.

## See also

`close printer`

## Name

open window — open a graphic window

## Synopsis

    open window x,y
    open window x,y,"font"

## Description

The `open window`-command opens a window of the specified size. Only one window can be opened at any given moment of time.

An optional third argument specifies a font to be used for any text within the window. It can however be changed with any subsequent `text`-command.

## Example

    for a=200 to 400 step 10
      open window a,a
      for b=0 to a
        line 0,b to a,b
        line b,0 to b,a
      sleep 0.1
      close window
    next a

## See also

`close window`, `text`

## Name

or — logical or, used in conditions

## Synopsis

    if (a or b) …
    while (a or b) …

## Description

Used in conditions (e.g within `if` or `while`) to join two expressions. Returns `true`, if either its left or its right or both arguments are `true`; returns `false` otherwise.

## Example

    input "Please enter a number"
    if (a>9 or a<1) print "a is not between 1 and 9"

## See also

`and`,`not`

## Name

or() — arithmetic or, used for bit-operations

## Synopsis

    x=or(a,b)

## Description

Used to compute the bitwise `or` of both its argument. Both arguments are treated as binary numbers (i.e. a series of 0 and 1); a bit of the resulting value will then be 1, if any of its arguments has 1 at this position in their binary representation.

Note, that both arguments are silently converted to integer values and that negative numbers have their own binary representation and may lead to unexpected results when passed to `or`.

## Example

    print or(14,3)

This will print `15`. This result is clear, if you note, that the binary representation of 14 and 3 are 1110 and 0011 respectively; this will yield 1111 in binary representation or 15 as decimal.

## See also

`oand`, `eor` and `not`

### P

## Name

pause — pause, sleep, wait for the specified number of seconds

## Synopsis

    pause 5

## Description

The `pause`-command has many different names: You may write `pause`, `sleep` or `wait` interchangeably; whatever you write, yabasic will always do exactly the same.

The `pause`-command will simply wait for the specified number of seconds. This may be a fractional number, so you may well wait less than a second. However, if you try to pause for a smaller and smaller interval (e.g. 0.1 seconds, 0.01 seconds, 0.001 seconds and so on) you will find that at some point yabasic will not wait at all. The minimal interval that can be waited depends on the system (Unix, Windows) you are using.

The `pause`-command cannot be interrupted. However, sometimes you may want the wait to be interruptible by simply pressing a key on the keyboard. In such cases you should consider using the `inkey$`-function, with a number of seconds as an argument).

## Example

    deg=0
    do
      maxx=44+40*sin(deg)
      for x=1 to maxx
        print "*";
      next x
      pause 0.1+(maxx*maxx/(4*84*84))
      print
      deg=deg+0.1
    loop

This example draws a sine-curve; due to the `pause`-statement the speed of drawing varies in the same way as the speed of a ball might vary, if it would roll along this curve under the influence of gravity.

## See also

`sleep`, `wait`

## Name

peek — retrieve various internal informations

## Synopsis

    print peek("foo")
    a=peek(#1)

## Description

The `peek`-function has many different and mostly unrelated uses. It is a kind of grabbag for retrieving all kinds of numerical information, internal to yabasic. The meaning of the numbers returned be the `peek`-function depends on the string or number passed as an argument.

`peek` always returns a number, however the closely related `peek$`-function exists, which may be used to retrieve string information from among the internals of yabasic. Finally note, that some of the values which are retrieved with `peek` may even be changed, using the `poke`-function.

There are two variants of the `peek`-function: One expects an integer, positive number and is described within the first entry of the list below. The other variant expects one of a well defined set of strings as described in the second and all the following entries of the list below.

`peek(a), peek(#a)`

  Read a single character from the file `a` (which must be open of course).

`peek("winheight")`

  Return the height of the graphic-window in pixels. If none is open, this `peek` will return the height of the last window opened or 100, if none has been opened yet.

`peek("winwidth")`

  Return the width of the graphic-window in pixels. If none is open, this `peek` will return the width of the last window opened or 100, if none has been opened yet.

`peek("fontheight")`

  Return the height of the font used within the graphic window. If none is open, this `peek` will return the height of the last font used or 10, if no window has been opened yet.

`peek("screenheight")`

  Return the height in characters of the window, wherein yabasic runs. If you have not called `clear screen` yet, this `peek`will return 0, regardless of the size of your terminal.

`peek("screenwidth")`

  Return the width in characters of the window, wherein yabasic runs. If you have not called `clear screen` yet, this `peek`will return 0, regardless of the size of your terminal.

`peek("argument")`

  Return the number of arguments, that have been passed to yabasic at invocation time. E.g. if yabasic has been called like this: `yabasic foo.yab bar baz`, then `peek("argument")` will return 2. This is because `foo.yab` is treated as the name of the program to run, whereas `bar` and `baz` are considered arguments to the program, which are passed on the commandline. Note, that for windows-users, who tend to click on the icon (as opposed to starting yabasic on the command line), this `peek`will mostly return 0.

  The function `peek("argument")` can be written as `peek("arguments")` too.

  You will want to check out the corresponding function `peek$("argument")` to actually retrieve the arguments. Note, that each call to `peek$("argument")` reduces the number returned by `peek("argument")`.

`peek("isbound")`

  Return `true`, if the executing yabasic-program is part of a standalone program; see the section about creating a standalone-program for details.

`peek("version")`

  Return the version number of yabasic (e.g. 2.72).

`peek("error")`

  Return a number specifying the nature of the last error in an `open`- or `seek`-statement. Normally an error within an `open`-statement immediately terminates your program with an appropriate error-message, so there is no chance and no need to learn more about the nature of the error. However, if you use `open` as a condition (e.g. `if (open(#1,"foo")) …`) the outcome (success or failure) of the `open`-operation will determine, if the condition evaluates to `true` or `false`. If now such an operation fails, your program will not be terminated and you might want to learn the reason for failure. This reason will be returned by `peek("error")` (as a number) or by `peek$("error")` (as a string)

  The table below shows the various error codes; the value returned by `peek$("error")` explains the nature of the error. Note, that the codes 10,11 and 12 refer to the `seek`-command.

  Table 6.1. Error codes

  `peek("error")` | `peek$("error")` | Explanation
  --- | --- | ---
  2 | `Stream already in use` | Do not try to open one and the same filenumber twice; rather `close` it first.
  3 | `'x' is not a valid filemode` | The optional filemode argument, which may be passed to the `open`-function, has an invalid value
  4 | `could not open 'foo'` | The `open`-call did not work, no further explanation is available.
  5 | `reached maximum number of open files` | You have opened more files than your operating system permits.
  6 | `cannot open printer: already printing graphics` | The commands `open printer` and `open #1,printer` both open a printer (refer to their description for the difference). However, only one can be active at a time; if you try to do both at the same time, you will receive this error.
  7 | `could not open line printer` | Well, it simply did not work.
  9 | `invalid stream number` | An attempt to use an invalid (e.g. negative) stream number; example: `open(-1,"foo")`
  10 | `could not position stream x to byte y` | `seek` did not work.
  11 | `stream x not open` | You have tried to `seek` within a stream, that has not been opened yet.
  12 | `seek mode 'x' is none of begin,end,here` | The argument, which has been passed to `seek` is invalid.

## Example

    open "foo" for reading as #1
    open "bar" for writing as #2
    while(not eof(#1))
      poke #2,chr$(peek(#1));
    wend

This program will copy the file `foo` byte by byte to `bar`.

Note, that each `peek` does something entirely different, and only one has been demonstrated above. Therefore you need to make up examples yourself for all the other `peek`s.

## See also

`peek$`, `poke`, `open`

## Name

peek$ — retrieve various internal string-informations

## Synopsis

    print peek$("foo")

## Description

The `peek$`-function has many different and unrelated uses. It is a kind of grabbag for retrieving all kinds of string information, internal to yabasic; the exact nature of the strings returned be the `peek$`-function depends on the string passed as an argument.

`peek$` always returns a string, however the closely related `peek`-function exists, which may be used to retrieve numerical information from among the internals of yabasic. Finally note, that some of the values which are retrieved with `peek$` may even be changed, using the `poke`-function.

The following list shows all possible arguments to `peek$`:

`peek$("infolevel")`

  Returns either `"debug"`, `"note"`, `"warning"`, `"error"` or `"fatal"`, depending on the current infolevel. This value can be specified with an option (either under windows or unix) on the commandline or changed during the execution of the program with the corresponding `poke`; however, normally only the author of yabasic (me !) would want to change this from its default value `"warning"`.

`peek$("textalign")`

  Returns one of nine possible strings, specifying the default alignment of text within the graphics-window. The alignment-string returned by this `peek` describes, how the `text`-command aligns its string-argument with respect to the coordinates supplied. However, this value does not apply, if the `text`-command explicitly specifies an alignment. Each of these strings is two characters long. The first character specifies the horizontal alignment and can be either `l`, `r` or `c`, which stand for left, right or center. The second character specifies the vertical alignment and can be one of `t`, `b` or `c`, which stand for top, bottom or center respectively.

  You may change this value with the corresponding command `poke "textalign",…`; the initial value is `lb`, which means the top of the left and the top edge if the text will be aligned with the coordinates, that are specified within the `text`-command.

`peek$("windoworigin")`

  This `peek` returns a two character string, which specifies the position of the origin of the coordinate system of the window; this string might be changed with the corresponding command `poke "windoworigin",x,y` or specified as the argument of the `origin` command; see there for a detailed description of the string, which might be returned by this `peek`.

`peek$("error")`

  Return a string describing the nature of the last error in an `open`- or `seek`-statement. See the corresponding `peek("error")` for a detailed description.

`peek$("library")`

  Return the name of the library, this statement is contained in. See the `import`-command for a detailed description or for more about libraries.

`peek$("os")`

  This `peek` returns the name of the operating system, where your program executes. This can be either `windows` or `unix`.

`peek$("font")`

  Return the name of the font, which is used for text within the graphic window; this value can be specified as the third argument to the `open window`-command.

`peek$("env","`NAME`")`

  Return the environment variable specified by `NAME` (which may be any string expression). Which kind of environment variables are available on your system depends, as well as their meaning, on your system; however typing env on the commandline will produce a list (for Windows and Unix alike). Note, that `peek$("env",...)` can be written as `peek$("environment",...)` too.

`peek$("argument")`

  Return one of the arguments, that have been passed to yabasic at invocation time (the next call will return the the second argument, and so on). E.g. if yabasic has been called like this: `yabasic foo.yab bar baz`, then the first call to `peek$("argument")` will return `bar`. This is because `foo.yab` is treated as the name of the program to run, whereas `bar` and `baz` are considered arguments to this program, which are passed on the commandline. The second call to `peek$("argument")` will return `baz`. Note, that for windows-users, who tend to click on the icon (as opposed to starting yabasic on the command line), this `peek`will mostly return the empty string.

  Note, that `peek$("argument")` can be written as `peek$("arguments")`.

  Finally you will want to check out the corresponding function `peek("argument")`.

## Example

    print "You have supplied these arguments: "
    while(peek("argument"))
      print peek("argument"),peek$("argument")
    wend

If you save this program in a file `foo.yab` and execute it via `yabasic t.yab a b c` (for windows users: please use the commandline for this), your will get this output:

    3a
    2b
    1c

## See also

`peek`, `poke`, `open`

## Name

pi — a constant with the value `3.14159`

## Synopsis

    print pi

## Description

`pi` is `3.14159265359` (well at least for yabasic); do not try to assign to pi (e.g. `pi=22/7`) this would not only be mathematically dubious, but would also result in a syntax error.

## Example

    for a=0 to 180
      print "The sine of ",a," degrees is ",sin(a*pi/180)
    next a

This program uses `pi` to transform an angle from degrees into radians.

## See also

`euler`

## Name

poke — change selected internals of yabasic

## Synopsis

    poke "foo","bar"
    poke "foo",baz
    poke #a,"bar"
    poke #a,baz

## Description

The `poke`-command may be used to change details of yabasic's behaviour. Like the related function `peek`, `poke` does many different things, depending on the arguments supplied.

Here are the different things you can do with `poke`:

`poke "textalign","cc"`

  This `poke` changes the default alignment of text with respect to the coordinates supplied within the `text`-command. However, this value does not apply, if the `text`-command explicitly specifies an alignment. The second argument (`"cc"` in the example) must always be two characters long; the first character can be one of `l` (left), `r` (right) or `c` (center); the second character can be either `t` (top), `b` (bottom) or `c` (center); see the corresponding `peek$("textalign")` for a detailed description of this argument.

`poke "windoworigin","lt"`

  This `poke` moves the origin of the coordinate system of the window to the specified position. The second argument (`"lt"` in the example) must always be two characters long; the first character can be one of `l` (left), `r` (right) or `c` (center); the second character can be either `t` (top), `b` (bottom) or `c` (center). Together those two characters specify the new position of the coordinate-origin. See the corresponding `peek$("windoworigin")` for a more in depth description of this argument.

`poke "infolevel","debug"`

  Change the amount of internal information, that yabasic outputs during execution.

  The second argument can be either `"debug"`, `"note"`, `"warning"`, `"error"` or `"fatal"`. However, normally you will not want to change this from its default value `"warning"`.

  See also the related `peek$("infolevel")`.

`poke #1,a`

  Write the given byte (`a` in the example above) to the specified stream (`#a` in the example).

  See also the related function function `peek(#1)`.

## Example

    print "Hello, now you will see, how much work"
    print "a simple for-loop involves ..."
    input "Please press return " a$
    poke "infolevel","debug"
    for a=1 to 10:next a

This example only demonstrates one of the many `poke`s, which are described above: The program switches the infolevel to `debug`, which makes yabasic produce a lot of debug-messages during the subsequent `for`-loop.

## See also

`peek`, `peek$`

## Name

print — Write to terminal or file

## Synopsis

    print "foo",a$,b
    print "foo","a$,b;
    print #a "foo",a$
    print #a "foo",a$;
    print foo using "##.###"
    print reverse "foo"
    print at(10,10) a$,b
    print @(10,10) a$,b
    print color("red","blue") a$,b
    print color("magenta") a$,b
    print color("green","yellow") at(5,5) a$,b

## Description

The `print`-statement outputs strings or characters, either to your terminal (also known as console) or to an open file.

To understand all those uses of the `print`-statement, let's go through the various lines in the synopsis above:

`print "foo",a$,b`

  Print the string `foo` as well as the contents of the variables `a$` and `b` onto the screen, silently adding a newline.

`print "foo",a$,b;`

  (Note the trailing semicolon !) This statement does the same as the one above; only the implicit newline is skipped, which means that the next `print`-statement will append seamlessly.

`print #a "foo",a$`

  This is the way to write to files. The file with the number `a` must be open already, an implicit newline is added. Note the file-number `#a`, which starts with a hash ('`#`') amd is separated from the rest of the statement by a space only. The file-number (contained in the variable `a`) must have been returned by a previous `open`-statement (e.g. `a=open("bar")`).

`print #a "foo",a$;`

  The same as above, but without the implicit newline.

`print foo using "##.###"`

  Print the number `foo` with as many digits before and after the decimal dot as given by the number of '`#`'-signs. See the entries for `using` and `str$` for a detailed description of this format.

`print reverse "foo"`

  As all the `print`-variants to follow, this form of the `print`-statement can only be issued after `clear screen` has been called. The strings and numbers after the `reverse`-clause are simply printed inverse (compared to the normal `print`-statement).

`print at(10,10) a$,b`

  Print at the specified (x,y)-position. This is only allowed after `clear screen` has been called. You may want to query `peek$("screenwidth")` or `peek$("screenheight")` to learn the actual size of your screen. You may add a semicolon to suppress the implicit newline.

`print @(10,10) a$,b`

  This is exactly the same as above, however, `at` may be written as `@`.

`print color("red","blue") at(5,5) a$,b`

  Print with the specified fore- (`"red"`) and background (`"blue"`) color (or colour). The possible values are `"black"`, `"white"`, `"red"`, `"blue"`, `"green"`, `"yellow"`, `"cyan"` or `"magenta"`. Again, you need to call `clear screen` first and add a semicolon if you want to suppress the implicit newline.

`print color("magenta") a$,b`

  You may specify the foreground color only.

`print color("green","yellow") a$,b`

  A color and a position (in this sequence, not the other way around) may be specified at once.

## Example

    clear screen
    columns=peek("screenwidth")
    lines=peek("screenheight")
    dim col$(7)
    for a=0 to 7:read col$(a):next a
    data "black","white","red","blue","green","yellow","cyan","magenta"

    for a=0 to 2*pi step 0.1
      print colour(col$(mod(i,8))) at(columns*(0.8*sin(a)+0.9)/2,lines*(0.8*cos(a)+0.9)/2) "*"
      i=i+1
    next a

This example draws a colored ellipse within the text window.

## See also

`at``, `print color`, input`, `clear screen`, `using`, `;`

## Name

print color — print with color

## Synopsis

    print color(fore$) text$
    print color(fore$,back$) text$

## Description

Not a separate command, but part of the `print`-command; may be included just after `print` and can only be issued after `clear screen` has been executed.

`color()` takes one or two string-arguments, specifying the color of the text and (optionally) the background.

The one or two strings passed to `color()` can be one of these: `"black"`, `"white"`, `"red"`, `"blue"`, `"green"`, `"yellow"`, `"cyan"` and `"magenta"` (which can be abbreviated as `"bla"`, `"whi"`, `"red"`, `"blu"`, `"gre"`, `"yel"`, `"cya"` and `"mag"` respectively).

`color()` can only be used, if `clear scren` has been issued at least once.

Note, that `color()` can be written as `colour()` too.

## Example

    clear screen
    dim col$(7):for a=0 to 7:read col$(a):next a
    do
      print color(col$(ran(7)),col$(ran(7))) " Hallo ";
      pause 0.01
    loop
    data "black","white","red","blue"
    data "green","yellow","cyan","magenta"

This prints the word `" Hallo "` in all colors across your screen.

## See also

`print`, `clear screen`, `at`

## Name

print colour — see `color`

## Synopsis

    print colour(fore$) text$
    print colour(fore$,back$) text$

## See also

`color`

## Name

putbit — draw a rectangle of pixels encoded within a string into the graphics window

## Synopsis

    open window 200,200
    …
    a$=getbit(20,20,50,50)
    …
    putbit a$,30,30
    putbit a$ to 30,30
    putbit a$,30,30,"or"

## Description

The `putbit`-command is the counterpart of the `getbit`-function. `putbit` requires a string as returned by the `getbit`-function. Such a string contains a rectangle from the graphic window; the `putbit`-function puts such a rectangular region back into the graphic-window.

Note, that the `putbit`-command currently accepts a third argument. However only the string value `"or"` is supported here. The effect is, that only those pixel, which are set in the string will be set in the graphic window. Those pixels, which are not set in the string, will not change in the window (as opposed to being cleared).

Note, that the format of the string returned by this function is due to change as soon as yabasic will learn, how to deal with colors.

## Example

    c$="rgb 21,21:0000000000000000000000000000000000000000000000000000000000000032c80000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000032c80032c80032c80032c80032c80032c80032c80032c80032c80000000000000000000000000000000000000000000000000000000000000032c80032c80032c80032c80032c80032c80032c80032c80032c80032c80032c80032c80000000000000000000000000000000000000000000000000032c80032c80032c80032c80032c80032c80032c80032c80032c80032c80032c80032c80032c80032c80032c80000000000000000000000000000000032c80032c80032c80032c80032c80032c80032c80032c8c8ff000032c80032c80032c80032c80032c80032c80032c80000000000000000000000000000000032c80032c80032c80032c80032c8c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff000032c80032c80032c80032c80032c80000000000000000000032c80032c80032c80032c80032c8c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff000032c80032c80032c80032c80032c80000000000000032c80032c80032c80032c8c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff000032c80032c80032c80032c80000000000000032c80032c80032c80032c8c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff000032c80032c80032c80032c80000000000000032c80032c80032c80032c8c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff000032c80032c80032c80032c80000000032c80032c80032c80032c8c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff000032c80032c80032c80032c80000000000000032c80032c80032c80032c8c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff000032c80032c80032c80032c80000000000000032c80032c80032c80032c8c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff000032c80032c80032c80032c80000000000000032c80032c80032c80032c8c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff000032c80032c80032c80032c80000000000000032c80032c80032c80032c80032c8c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff000032c80032c80032c80032c80032c80000000000000000000032c80032c80032c80032c80032c8c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff000032c80032c80032c80032c80032c80000000000000000000000000032c80032c80032c80032c80032c80032c80032c80032c80032c80032c80032c80032c80032c80032c80032c80032c80000000000000000000000000000000000000032c80032c80032c80032c80032c80032c80032c80032c80032c80032c80032c80032c80032c80032c80032c80000000000000000000000000000000000000000000032c80032c80032c80032c80032c80032c80032c80032c80032c80032c80032c80032c80000000000000000000000000000000000000000000000000000000000000000000032c80032c80032c80032c80032c80032c80032c80032c80032c8000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"

    open window 200,200

    do
      x=ran(220)-10
      y=ran(220)-10
      putbit c$,x,y,"transparent"
    loop

This program uses a precanned string (containing the image of a blue circle with a yellow centre) and draws it repeatedly into the graphic-window. The mode `"transparent"` ensures, that no pixels will be cleared.

There are two possible values for the third argument of `putbit`. Both modes differ in the way, they replace (or not) any pixels from the window with pixels from the bitmap having the background colour.

`transparent` or `t`

  With this mode the pixels from the window will be kept, if the bitmap contains pixels with background colour at this position; i.e. the bitmap is transparent

`solid` or `s`

  With this mode the pixels from the window will be overpainted with the pixels from the bitmap in any case; i.e. the bitmap is solid

If you omit this argument, the default `transparent` applies.

## See also

`getbit$`, `open window`

## Name

putscreen — draw a rectangle of characters into the text terminal

## Synopsis

    clear screen
    …
    a$=getscreen$(5,5,10,10)
    …
    putscreen a$,7,7

## Description

The `putscreen`-command is the counterpart of the `getscreen$`-function. `putscreen` requires a string as returned by the `getscreen`-function. Such a string contains a rectangular detail from the terminal; the `putscreen`-function puts such a region back into the terminal-window.

Note, that `clear screen` must have been called before.

## Example

    clear screen
    for a=1 to 200
      print color("red") "Hallo !";
      print color("blue") "Welt !";
    next a
    r$=getscreen$(0,0,20,20)
    for x=0 to 60
      putscreen r$,x,0
      sleep 0.1
    next x

This example prints the string `"Hallo !Welt !"` all over the screen and then moves a rectangle from one side to the other.

## See also

`getscreen$`, `clear screen`

### R

## Name

ran() — return a random number

## Synopsis

    print ran()
    x=ran(y)

## Description

The `ran`-function returns a random number. If no argument is given, the number returned is in the range from 0 to 1; where only 0 is a possible value; 1 will never be returned. If an argument is supplied, the number returned will be in the range from 0 up to this argument, whereas this argument itself is not a possible return value.

## Example

    clear screen
    c=peek("screenwidth")-1
    l=peek("screenheight")

    dim col$(8)
    for a=0 to 7:read col$(a):next a
    data "black","white","red","blue","green","yellow","cyan","magenta"

    do
      x=ran(c)
      y=l-ran(l*exp(-32*((x/c-1/2)**2)))
      i=i+1
      print color(col$(mod(i,8))) at(x,y) "*";
    loop

This example will print a cloured bell-curve.

## See also

`int`

## Name

read — read data from `data`-statements

## Synopsis

    read a$,a
    …
    data "Hello !",7

## Description

The `read`-statement retrieves literal data, which is stored within `data`-statements elsewhere in your program.

## Example

    read num
    dim col$(num)
    for a=1 to num:read col$(a):next a
    clear screen
    print "These are the colours known to yabasic:\n"
    for a=1 to num
      print colour(col$(a)) col$(a)
    next a

    data 8,"black","white","red","blue"
    data "green","yellow","cyan","magenta"

This program prints the names of the colors known to yabasic in those very colors.

## See also

`data, `restore``

## Name

rectangle — draw a rectangle

## Synopsis

    open window 100,100
    rectangle 10,10 to 90,90
    rectangle 20,20,80,80
    rect 20,20,80,80
    box 30,30,70,70
    clear rectangle 30,30,70,70
    fill rectangle 40,40,60,60
    clear fill rectangle 60,60,40,40

## Description

The `rectangle`-command (also known as `box` or `rect`, for short) draws a rectangle; it accepts four parameters: The x- and y-coordinates of two facing cornerpoints of the rectangle. With the optional clauses `clear` and `fill` (which may appear both and in any sequence) the rectangle can be cleared and filled respectively.

## Example

    open window 200,200
    c=1
    do
      for phi=0 to pi step 0.1
        if (c) then
          rectangle 100+100*sin(phi),100+100*cos(phi) to 100-100*sin(phi),100-100*cos(phi)
        else
          clear rectangle 100+100*sin(phi),100+100*cos(phi) to 100-100*sin(phi),100-100*cos(phi)
        endif
        sleep 0.1
      next phi
      c=not c
    loop

This example draws a nice animated pattern; watch it for a couple of hours, to see how it develops.

## See also

`open window`, `open printer`, `line`, `circle`, `triangle`

## Name

redim — create an array prior to its first use. A synonym for `dim`

## Synopsis

    See the dim-command.

## Description

The `redim`-command does exactly the same as the `dim`-command; it is just a synonym. `redim` has been around in older versions of basic (not even yabasic) for many years; therefore it is supported in yabasic for compatibility reasons.

Please refer to the entry for the `dim`-command for further information.

## Name

rem — start a comment

## Synopsis

    rem  Hey, this is a comment
    #    this is a comment too
    // even this
    print "Not a comment" #    This is an error !!
    print "Not a comment"://   But this is again a valid comment
    print "Not a comment" //   even this.
    print "Not a comment" rem  and this !

## Description

`rem` introduces a comment (like `#` or `//`), that extends up to the end of the line.

Those comments do not even need a colon ('`:`') in front of them; they (`rem`, `#` and `//`) all behave alike except for `#`, which may only appear at the very beginning of a line; therefore the fourth example in the synopsis above (`print "Not a comment" # This is an error !!`) is indeed an error.

Note, that `rem` is an abbreviation for remark. `remark` however is not a valid command in yabasic.

Finally note, that a comment introduced with '`#`' may have a special meaning under unix; see the entry for # for details.

## Example

    #
    rem   comments on data structures
    #     are more useful than
    //    comments on algorithms.
    rem

This program does nothing, but in a splendid and well commented way.

## See also

`#`, `//`

## Name

repeat — start a `repeat`-loop

## Synopsis

    repeat
      …
    until (…)

## Description

The `repeat`-loop executes all the statements up to the final `until`-keyword over and over. The loop is executed as long as the condition, which is specified with the `until`-clause, becomes true. By construction, the statements within the loop are executed at least once.

## Example

    x=0
    clear screen
    print "This program will print the numbers from 1 to 10"
    repeat
      x=x+1
      print x
      print "Press any key for the next number, or 'q' to quit"
      if (inkey$="q") break
    until(x=10)

This program is pretty much useless, but self-explanatory.

## See also

`until`, `break`, `while`, `do`

## Name

restore — reposition the `data`-pointer

## Synopsis

    read a,b,c,d,e,f
    restore
    read g,h,i
    restore foo
    data 1,2,3
    label foo
    data 4,5,6

## Description

The `restore`-command may be used to reset the reading of `data`-statements, so that the next `read`-statement will read data from the first `data`-statement.

You may specify a label with the `restore`-command; in that case, the next `read`-statement will read data starting at the given label. If the label is omitted, reading data will begin with the first `data`-statement within your program.

## Example

    input "Which language (german/english) ? " l$
    if (instr("german",l$)>0) then
      restore german
    else
      restore english
    endif

    for a=1 to 3
      read x,x$
      print x,"=",x$
    next a

    label english
    data 1,"one",2,"two",3,"three"
    label german
    data 1,"eins",2,"zwei",3,"drei"

This program asks to select one of those languages known to me (i.e. english or german) and then prints the numbers 1,2 and 3 and their textual equivalents in the chosen language.

## See also

`read`, `data`, `label`

## Name

return — return from a subroutine or a gosub

## Synopsis

    gosub foo
    …
    label foo
    …
    return

    sub bar(baz)
      …
      return quertz
    end sub

## Description

The `return`-statement serves two different (albeit somewhat related) purposes. The probably more important use of `return` is to return control from within a subroutine to the place in your program, where the subroutine has been called. If the subroutine is declared to return a value, the `return`-statement might be accompanied by a string or number, which constitutes the return value of the subroutine.

However, even if the subroutine should return a value, the `return`-statement need not carry a value; in that case the subroutine will return 0 or the empty string (depending on the type of the subroutine). Moreover, feel free to place multiple `return`-statements within your subroutine; it's a nice way of controlling the flow of execution.

The second (but historicially first) use of `return` is to return to the position, where a prior `gosub` has left off. In that case `return` may not carry a value.

## Example

    do
      read a$
      if (a$="") then
        print
        end
      endif
      print mark$(a$)," ";
    loop

    data "The","quick","brown","fox","jumped"
    data "over","the","lazy","dog",""

    sub mark$(a$)
      if (instr(lower$(a$),"q")) return upper$(a$)
      return a$
    end sub

This example features a subroutine `mark$`, that returns its argument in upper case, if it contains the letter "q", or unchanged otherwise. In the test-text the word `quick` will end up being marked as `QUICK`.

The example above demonstrates `return` within subroutines; please see `gosub` for an example of how to use `return` in this context.

## See also

`sub`, `gosub`

## Name

reverse — print reverse (background and foreground colors exchanged)

## Synopsis

    clear screen
    …
    print reverse "foo"

## Description

`reverse` may be used to `print` text in reverse. `reverse` is not a separate command, but part of the `print`-command; it may be included just after the `print` and can only be issued once that `clear screen` has been issued.

## Example

    clear screen

    print "1 ";
    c=3
    do
      prim=true
      for a=2 to sqrt(c)
        if (frac(c/a)=0) then
          prim=false
          break
        endif
      next a
      if (prim) then
        print
        print reverse c;
      else
        print c;
      endif
      print " ";
      c=c+1
    loop

This program prints numbers from 1 on and marks each prime number in reverse.

## See also

`at``, `print color`, print`, `clear screen`

## Name

right$() — return (or change) the right end of a string

## Synopsis

    print right$(a$,2)
    right$(b$,2)="baz"

## Description

The `right$`-function requires two arguments (a string and a number) and returns the part from the right end of the string, whose length is specified by its second argument. So, `right$` simply returns the requested number of chars from the right end of the given string.

Note, that the `right$`-function can be assigned to, i.e. it may appear on the left hand side of an assignment. In this way it is possible to change a part of the variable used within the `right$`-function. Note, that that way the length of the string cannot be changed, i.e. characters might be overwritten, but not added. For an example see below.

## Example

    print "Please enter a length either in inch or centimeter"
    print "please add 'in' or 'cm' to mark the unit."
    input "Length: " a$
    if (right$(a$,2)="in") then
       length=val(a$)*2.56
    elsif (right$(a$,2)="cm") then
       length=val(a$)
    else
       error "Invalid input: "+a$
    endif

This program allows the user to enter a length qualified with a unit (either inch or centimeter).

This second example demonstrates the capability to assign to the `right$`-function.

    a$="Heiho World !"
    print a$
    right$(a$,7)="dwarfs."
    print a$

## See also

`right$` and `mid$`

## Name

rinstr() — find the rightmost occurrence of one string within the other

## Synopsis

    pos=rinstr("Thequickbrownfox","equi")
    pos=rinstr(a$,b$,x)

## Description

The `rinstr`-function accepts two string-arguments and tries to find the second within the first. However, unlike the `instr`, the `rinstr`-function finds the rightmost (or last) occurrence of the string; whereas the `instr`-function finds the leftmost (or first) occurrence. In any case however, the position is counted from the left.

If you supply a third, numeric argument to the `rinstr`-function, it will be used as a starting point for the search. Therefore `rinstr("abcdeabcdeabcde","e",8)` will return 5, because the search for an "`e`" starts at position 8 and finds the first one at position 5.

## Example

    print rinstr("foofoofoobar","foo")

This simple example will print `7`, because it finds the rightmost among the three occurrences of `foo` within the string. Note, that

    print instr("foofoofoobar","foo")

would have printed `1`.

## See also

`instr`

## Name

rtrim$() — trim spaces at the right end of a string

## Synopsis

    a$=rtrim$(b$)

## Description

The `rtrim$`-function removes all whitespace from the right end of a string and returns the result.

## Example

    open 1,"foo"
    dim lines$(100)
    l=1
    while(not eof(1))
      input #1 a$
      a$=rtrim$(a$)
      if (right$(line$,1)="\\") then
        line$=line$+" "+a$
      else
        lines$(l)=line$
        l=l+1
        line$=a$
      endif
    end while
    print "Read ",l," lines"

This example reads the file `foo` allowing for continuation lines, which are marked by a `\`, which appears as the last character on a line. For convenience whitespace at the right end of a line is trimmed with `rtrim`.

## See also

`ltrim$`, `trim$`

### S

## Name

screen — as `clear screen` clears the text window

## Synopsis

    clear screen

## Description

The keyword `screen` appears only within the sequence `clear screen`; please see there for a description.

## See also

`clear screen`

## Name

seek() — change the position within an open file

## Synopsis

    open 1,"foo"
    seek #1,q
    seek #1,x,"begin"
    seek #1,y,"end"
    seek #1,z,"here"

## Description

The `seek`-command changes the position, where the next `input` (or `peek`) statement will read from an open file. Usually files are read from the beginning to the end sequentially; however sometimes you may want to depart from this simple scheme. This can be done with the `seek`-command, allowing you to change the position, where the next piece of data will be read from the file.

`seek` accepts two or three arguments: The first one is the number of an already open file. The second one is the position where the next read from the file will start. The third argument is optional and specifies the the point from where the position (the second argument) will count. It can be one of:

`begin`

  Count from the beginning of the file.

`end`

  Count from the end of the file.

`here`

  Count from the current position within the file.

## Example

    open #1,"count.dat","w"
    for a=1 to 10
      print #1,"00000000";
      if (a<10) print #1,";";
    next a

    dim count(10)
    do
      x=int(ran(10))
      i=i+1
      if (mod(i,1000)=0) print ".";
      count(x)=count(x)+1
      curr$=right$("00000000"+str$(count(x)),8)
      seek #1,9*x,"begin"
      print #1,curr$;
    loop

This example increments randomly one of ten counters (in the array `count()`); however, the result is always kept and updated within the file `count.dat`, so even in case of an unexpected interrupt, the result will not be lost.

## See also

`tell`, `open`, `print`, `peek`

## Name

sig() — return the sign of its argument

## Synopsis

    a=sig(b)

## Description

Return `+1`, `-1` or `0`, if the single argument is positive, negative or zero.

## Example

    clear screen
    dim c$(3):c$(1)="red":c$(2)="white":c$(3)="green"
    do
      num=ran(100)-50
      print color(c$(2+sig(num))) num
    loop

This program prints an infinite sequence of random number; positive numbers are printed in green, negative numbers are printed red (an exact zero would be printed white). (With a little extra work, this program could be easily extended into a brokerage system)

## See also

`abs`, `int`, `frac`

## Name

sin() — return the sine of its single argument

## Synopsis

    y=sin(angle)

## Description

The `sin`-function expects an angle (in radian, not degree) and returns its sine.

## Example

    open window 200,200
    new curve
    for phi=0 to 2*pi step 0.1
      line to 100+90*sin(phi),100+90*cos(phi)
    next phi
    close curve

This program draws a circle (ignoring the existence of the `circle`-command).

## See also

`asin`, `cos`

## Name

sleep — pause, sleep, wait for the specified number of seconds

## Synopsis

    sleep 4

## Description

The `sleep`-command has many different names: You may write `pause`, `sleep` or `wait` interchangable; whatever you write, yabasic will always do exactly the same.

Therefore you should refer to the entry for the `pause`-function for further information.

## Name

split() — split a string into many strings

## Synopsis

    dim w$(10)
    …
    num=split(a$,w$())
    num=split(a$,w$(),s$)

## Description

The `split`-function requires a string (containing the text to be split), a reference to a string-array (which will receive the resulting strings, i.e. the tokens) and an optional string (with a set of characters, at which to split, i.e. the delimiters).

The `split`-function regards its first argument (a string) as a list of tokens separated by delimiters and it will store the list of tokens within the array-reference you have supplied. Note, that the array, which is passed as a reference (`w$()` in the synopsis), will be resized accordingly, so that you don't have to figure out the number of tokens in advance. The element at position zero (i.e. `w$(0)`) will not be used.

normally (i.e. if you omit the third, which is the delimiter-argument) the function will regard space or tab as delimiters for tokens; however by supplying a third argument, you may split at any single of the characters within this string. E.g. if you supply `":;"` as the third argument, then colon (`:`) or semicolon (`;`) will delimit tokens.

Note, that a sequence of separator-characters will produce a sequence of empty tokens; that way, the number of tokens returned will always be one plus the number of separator characters contained within the string. Refer to the closely related `token`-function, if you do not like this behaviour. In some way, the `split`-function focuses on the separators (other than the `token`-function, which focuses on the tokens), hence its name.

The second argument is a reference on a string-array, where the tokens will be stored; this array will be expanded (or shrinked) to have room for all tokens, if necessary.

The first argument finally contains the text, that will be split into tokens. The `split`-function returns the number of tokens that have been found.

Please see the examples below for some hints on the exact behaviour of the `split`-function and how it differs from the `token`-function:

## Example

    print "This program will help you to understand, how the"
    print "split()-function exactly works and how it behaves"
    print "in certain special cases."
    print
    print "Please enter a line containing tokens separated"
    print "by either '=' or '-'"
    dim t$(10)
    do
      print
      input "Please enter a line: " l$
      num=split(l$,t$(),"=-")
      print num," Tokens: ";
      for a=1 to num
        if (t$(a)="") then
          print "(EMPTY)";
        else
          print t$(a);
        endif
        if (a<num) print ",";
      next a
      print
    loop

This program prints the following output:

    Please enter a line: a
    1 Tokens: a

    Please enter a line:
    0 Tokens:

    Please enter a line: ab
    1 Tokens: ab

    Please enter a line: a=b
    2 Tokens: a,b

    Please enter a line: a-
    2 Tokens: a,(EMPTY)

    Please enter a line: a-=
    3 Tokens: a,(EMPTY),(EMPTY)

    Please enter a line: =a-
    3 Tokens: (EMPTY),a,(EMPTY)

    Please enter a line: a=-b
    3 Tokens: a,(EMPTY),b

    Please enter a line: a--b-
    4 Tokens: a,(EMPTY),b,(EMPTY)

    Please enter a line: -a==b-c==
    7 Tokens: (EMPTY),a,(EMPTY),b,c,(EMPTY),(EMPTY)

## See also

`token`

## Name

sqr() — compute the square of its argument

## Synopsis

    a=sqr(b)

## Description

The `sqr`-function computes the square of its numerical argument (i.e. it multiplies its argument with itself).

## Example

    for a=1 to 10
      print a,sqr(a),a**2
    next a

As you may see from the output, `sqr` can be written as `**2` (or `^2`) too.

## See also

`sqrt`, `**`, `^`

## Name

sqrt() — compute the square root of its argument

## Synopsis

    to be written

## Description

The `sqrt`-function computes the square root of its numerical argument.

## Example

    for a=1 to 5
      print a,sqrt(a),a**(1/2)
    next a

As you may see from the output, `sqrt` can be written as `**(1/2)` (or `^(1/2)`) too.

## See also

`sqr`, `**`, `^`

## Name

static — preserves the value of a variable between calls to a subroutine

## Synopsis

    sub foo()

      static a

      …

    end sub

## Description

The `static` keyword can be used within subroutines to mark variables as static. This has two effects: First, the variable is local to the subroutine, i.e. its value is not know outside the subroutine (this is the effect of the `local` keyword). Second, the `static`-keyword arranges things, so that the variable keeps its value between invocations of the subroutine (this is different from the `local`-keyword).

## Example

    foo()
    foo()
    foo()

    sub foo()
      static a
      local b
      a=a+1
      b=b+1
      print a,b
    end sub

This program shows the difference between `static` and `local` variables within a subroutine; it produces this output:

    1 1
    2 1
    3 1

The output shows, that the `static` variable `a` keeps its value between subroutine calls, whereas `b` is initialized with the value 0 at every call to the subroutine `foo`.

## See also

`sub`, `local`

## Name

step — specifies the increment step in a for-loop

## Synopsis

    for a=1 to 10 step 3
      …
    next a

## Description

Specify, by which amount the loop-variable of a `for`-loop will be incremented at each step.

The `step` (as well as the lower and upper bound) are computed anew in each step; this is not common, but possible, as the example below demonstrates.

## Example

    for x=1 to 1000 step y
      y=x+y
      print x," ",y," ";
    next x
    print

This program computes the fibonacci numbers between 1 and 1000.

## See also

`for`

## Name

str$() — convert a number into a string

## Synopsis

    a$=str$(a)
    b$=str$(x,"##.###")
    b$=str$(x,"###,###.##")
    b$=str$(x,"###,###.##","_.")

## Description

The `str$`-function accepts a numeric argument and returns it as a string. This conversion between number and string can be controlled with the optional third argument (the format argument). See the following table of examples to learn about valid values of this argument. Note, that those examples fall in one of two categories: C-style and basic-style; the first 4 examples in the table below are C-style, the rest of the examples are basic-style. For more information on the C-style formats, you may refer to your favorite documentation on the C programming language. The basic-style formats are much simpler, they just depict the desired output, marking digits with '`#`'; groups of (usually three) digits may be separated with colons ('`,`'), the decimal dot must be marked by a literal dot ('`.`'). Moreover these characters (colons and dot) may be replaced by other characters to satisfy the needs of non-english (e.g. german) languages; see the examples below.

Note, that for clarity, each space in the result has been replaced by the letter 'x', because it would be hard to figure out, how many spaces are produced exactly otherwise.

Table 6.2. Examples for the format argument

`Example string` | `Result for converting 1000*`pi`` | `Description`
--- | --- | ---
`%2.5f` | `3141.59265` | The '`2`' determines the minimum length of the output; but if needed (as in the example) the output can be longer. The '`5`' is the number of digits after the decimal point.
`%12.5f` | `xx3141.59265` | Two spaces (which appear as '`x`') are added to pad the output to the requested length of 12 characters.
`%012.5g` | `0000003141.6` | The '`g`' requests, that the precision ('`5`') specifies the overall number of digits (before and after the decimal point).
`%-12.5f` | `3141.59265xx` | The '`-`' requests the output to be left-centered (therefor the filling space appears at the right).
`#####.##` | `x3141.59` | Each '`#`' specifies a digit (either before or after the dot), the '`.`' specifies the position of the dot. As 1000*`pi` does not have enough digits, the 5 requested digits before the dot are filled up with a space (which shows up as an '`x`').
`##,###.##` | `x3,141.59` | Nearly the same as above, but the colon from the format shows up within the result.
`##,###.##` and an additional argument of `".,"` | `x3.141,59` | Similar to the example above, but colon and dot are replaced with dot and colon respectivly.
`##,###.##` and an additional argument of `"_,"` | `x3_141,59` | Similar to the example above, but colon and dot are replaced with underscore and colon respectivly.
`#####` | `x3142` | The format string does not contain a dot, and therefore the result does not have any fractional digits.
`##.###` | `##.###` | As 1000*`pi` has 4 digits in front of the decimal dot and the format only specifies 2, yabasic does not know what to do; therefore it chooses just to reproduce the format string.

## Example

    do
      input "Please enter a format string: " f$
      a$=str$(1000*pi,f$)
      for a=1 to len(a$)
        if (mid$(a$,a,1)=" ") mid$(a$,a,1)="x"
      next a
      print a$
    loop

This is the program, that has been used to get the results shown in the table above.

## See also

`print`, `using`

## Name

sub — declare a user defined subroutine

## Synopsis

    foo(2,"hello")

    …

    sub foo(bar,baz$)
      …
      return qux
      …
    end sub

## Description

The `sub`-keyword starts the definition of a user defined subroutine. With user defined subroutines you are able to somewhat extend yabasic with your own commands or functions. A subroutine accepts arguments (numbers or strings) and returns a number or a string (however, you are not required to assign the value returned to a variable).

The name of the subroutine follows after the keyword `sub`. If the name (in the synopsis: `foo`) ends on a '`$`', the subroutine should return a string (with the `return`-statement), otherwise a number.

After the name of the subroutine yabasic requires a pair of braces; within those braces you may specify a list of parameters, for which values can (but need not) be included when calling the subroutine. If you omit one of those parameters when calling such a subroutine, it assumes the value zero (for numeric parameters) or the empty string (for string-parameters). However from the special variable `numparams` you may find out, how many arguments have really been passed when calling the subroutine.

Parameters of a subroutine are always local variables (see the keyword `local` for more explanation).

From within the subroutine you may return any time with the keyword `return`; along with the `return`-keyword you may specify the return value. Note that more than one `return` is allowed within a single subroutine.

Finally, the keyword `end sub` ends the subroutine definition. Note, that the definition of a subroutine need not appear within the program before the first call to this sub.

### Note

As braces have two uses in yabasic (i.e. for supplying arguments to a subroutine as well as to list the indices of an array). yabasic can not tell apart an array from a subroutine with the same name. Therefore you cannot define a subroutine with the same name as an array !

## Example

    p=2
    do
      if (is_prime(p)) print p
      p=p+1
    loop

    sub is_prime(a)
      local b
      for b=2 to sqrt(a)
        if (frac(a/b)=0) return false
      next b
      return true
    end sub

This example is not the recommended way to compute prime numbers. However it gives a nice demonstration of using a subroutine.

## See also

`local`, `static`, `peek`

## Name

switch — select one of many alternatives depending on a value

## Synopsis

    switch a
      case 1
      case 2
      …
    end switch

    …

    switch a$
      case "a"
      case "b"
    end switch

## Description

The `switch`-statement selects one of many codepaths depending on a numerical or string expression. I.e. it takes an expression (either numeric or string) and compares it with a series of values, each wrapped within a `case`-clause. If the expression equals the value given in a `case`-clause, the subsequent statements are executed.

The `default`-clause allows to specify commands, which should be executed, if none of `case`-clauses matches.

Note, that many `case`-clauses might be clustered (e.g. `case "a":case "b":case "c"`). Or put another way: You need a `break`-statement at the end of a `case`-branch, if you do not want to run into the next `case`.

## Example

    input "Please enter a single digit: " n
    switch n
      case 0:print "zero":break
      case 1:print "one":break
      case 2:print "two":break
      case 3:print "three":break
      case 4:print "four":break
      case 5:case 6: case 7:case 8:case 9
        print "Much !":break
      default:print "Hey ! That was more than a single digit !"
    end switch

This example translates a single digit into a string; note, how the cases 5 to 7 are clustered.

## See also

`switch`, `case`, `break`

## Name

system$() — hand a statement over to your operating system and return its output

## Synopsis

    print system$("dir")

## Description

The `system$`-command accepts a single string argument, specifying a command, that can be found and executed by your operating system. It returns the output of this command as one big string.

## Example

    input "Please enter the name of a directory: " d$
    print
    print "This is the contents of the '"+d$+"':"
    print system$("dir "+d$)

This example lists the contents of a directory, employing the dir-command (which is about the only program, that is known under Unix as well as Windows).

## See also

`system`

## Name

system() — hand a statement over to your operating system and return its exitcode

## Synopsis

    ret=system("foo")
    system("bar")

## Description

The `system`-command accepts a single string argument, which specifies a command to be executed. The function will return the exitcode of the command; its output (if any) will be lost.

## Example

    print "Please enter the name of the file, that should be deleted."
    input f$
    if (system("rm "+f$+" >/dev/null 2>&1")) then
      print "Error !"
    else
      print "okay."
    endif

This program is Unix-specific: It uses the Unix-command `rm` to remove a file.

## See also

`system$`

### T

## Name

tan() — return the tangens of its argument

## Synopsis

    foo=tan(bar)

## Description

The `tan`-function computes the tangens of its arguments (which should be specified in radian).

## Example

    for a=0 to 45
      print tan(a*pi/180)
    next a

This example simply prints the tangens of all angles between 0 and 45 degree.

## See also

`atan`, `sin`

## Name

tell — get the current position within an open file

## Synopsis

    open #1,"foo"
      …
    position=tell(#1)

## Description

The `tell`-function requires the number of an open file as an argument. It returns the position (counted in bytes, starting from the beginning of the file) where the next read will start.

## Example

    open #1,"foo","w"
    print #1 "Hello World !"
    close #1

    open #1,"foo"
    seek #1,0,"end"
    print tell(#1)
    close 1

This example (mis)uses `tell` to get the size of the file. The `seek` positions the file pointer at the end of the file, therefor the call to `tell` returns the total length of the file.

## See also

`tell`, `open`

## Name

text — write text into your graphic-window

## Synopsis

    text x,y,"foo"
    text x,y,"foo","lb"
    text x,y,"foo","cc","font"
    text x,y,"foo","font","rt"

## Description

The `text`-commands displays a text-string (the third argument) at the given position (the first two arguments) within an already `open`ed `window`. The font to be used can be optionally specified as either the fourth or fifth argument (`"font"` in the example above). A font specified this way will also be used for any subsequent `text`-commands, as long as they do not specify a font themselves.

The fourth or fifth optional argument (`"lb"` in the example above) can be used to specify the alignment of the text with respect to the specified position. This argument is always two characters long: The first character specifies the horizontal alignment and can be either `l`, `r` or `c`, which stand for left, right or center. The second character specifies the vertical alignment and can be one of `t`, `b` or `c`, which stand for top, bottom or center respectively. If you omit this alignment argument, the default `"lb"` applies; however this default may be changed with `poke "textalign","xx"`

## Example

    open window 500,200
    clear screen
    data "lt","lc","lb","ct","cc","cb","rt","rc","rb"
    for a=1 to 9
      read align$
      print "Alignment: ",align$
      line 50*a-15,100,50*a+15,100
      line 50*a,85,50*a,115
      text 50*a,100,"Test",align$
      inkey$
    next a

This program draws nine crosses and writes the same text at each; however it goes through all possible nine alignment strings, showing their effect.

## See also

`open window`, `peek`, `poke`

## Name

then — tell the long from the short form of the `if`-statement

## Synopsis

    if (a<b) then
      …
    endif

## Description

The keyword `then` is part of the `if`-statement; please see there for further explanations. However, not every `if`-statement requires the keyword `then`: If the keyword `then` is present, the `if`-clause may extend over more than one line, and the keyword `endif` is required to end it. If the keyword `then` is not present, the `if`-statement extends up to the end of the line, and any `endif` would be an error.

## Example

    if (1<2) then
      print "Hello ";
    endif

    if (2<3) print "world"
    if (2<1)
      print "!"

This example prints `Hello world`. Note, that no exclamation mark (`!`) is printed, which might come as a surprise and may be changed in future versions of yabasic.

## See also

`if`

## Name

time$ — return a string containing the current time

## Synopsis

    print time$
    print time$()

## Description

The `time$` function returns the current time in four fields separated by hyphens '`-`'. The fields are:

- The current hour in the range from 0 to 23, padded with zeroes (e.g. `00` or `04`) to a length of two characters.

- The number of minutes, padded with zeroes.

- The number of seconds, padded with zeroes.

- The number of seconds, that have elapsed since the program has been started. This value increases as long as your program runs and is therefore unbound and not padded with zeroes.

At the time of writing this documentation, `time$` returns `22-58-53-0`. Note, that the first three of the four fields returned by `time$` have a fixed width; therefore it is easy to extract some fields with the usual string-functions `mid$` (and others).

## Example

    print "Hello it is ",time$
    print "An empty for-loop with ten million iterations takes ";
    s=val(mid$(time$,10))
    for a=1 to 10000000:next a
    e=val(mid$(time$,10))
    print e-s," seconds"

This program benchmarks the `for`-loop and uses the fourth field of the string returned by `time$`.

## See also

`date`

## Name

to — this keyword appears as part of other statements

## Synopsis

    for a=1 to 100 step 2
      …
    next a

    line x,y to a,b

## Description

The `to`-keyword serves two purposes (which are not related at all):

- within `for`-statements, to specify the upper bound of the loop.

- Within any graphical command (e.g. `line`), that requires two points (i.e. four numbers) as arguments, a comma '`,`' might be replaced with the keyword `to`. I.e. instead of `100,100,200,200` you may write `100,100 to 200,200` in such commands.

## Example

Please see the command listed under "See also" for examples.

## See also

`for`, `line`, `rectangle`

## Name

token() — split a string into multiple strings

## Synopsis

    dim w$(10)
    …
    num=token(a$,w$())
    num=token(a$,w$(),s$)

## Description

The `token`-function accepts a string (containing the text to be split), a reference to a string-array (which will receive the resulting strings, i.e. the tokens) and an optional string (with a set of characters, at which to split, i.e. the delimiters).

The `token`-function regards its first argument as a list of tokens separated by delimiters and it will store the list of tokens within the array-reference that has been supplied. Note, that the array, which is passed as a reference (`w$()` in the synopsis), will be resized accordingly, so that you don't have to figure out the number of tokens in advance. The element at position zero (i.e. `w$(0)`) will not be used.

Normally (i.e. if you omit the third, the delimiter-argument) the function will regard space or tab as delimiters for tokens; however by supplying a third argument, you may split at any single of the characters within this string. E.g. if you supply `":;"` as the third argument, then colon (`:`) or semicolon (`;`) will delimit tokens.

Note, that `token` will never produce empty tokens, even if two or more separators follow in sequence. Refer to the closely related `split`-function, if you do not like this behaviour. In some way, the `token`-function focuses on the tokens and not on the separators (other than the `split`-function, which focuses on the separators).

The second argument is a reference on a string-array, where the tokens will be stored; this array will be expanded (or shrinked) as necessary to have room for all tokens.

The first argument finally contains the text, that will be split into tokens. The `token`-function returns the number of tokens, that have been found.

Please see the examples below for some hints on the exact behaviour of the `token`-function and how it differs from the `split`-function:

## Example

    print "This program will help you to understand, how the"
    print "token()-function exactly works and how it behaves"
    print "in certain special cases."
    print
    print "Please enter a line containing tokens separated"
    print "by either '=' or '-'"
    dim t$(10)
    do
      print
      input "Please enter a line: " l$
      num=token(l$,t$(),"=-")
      print num," Tokens: ";
      for a=1 to num
        if (t$(a)="") then
          print "(EMPTY)";
        else
          print t$(a);
        endif
        if (a<num) print ",";
      next a
      print
    loop

This program prints the following output:

    Please enter a line: a
    1 Tokens: a

    Please enter a line:
    0 Tokens:

    Please enter a line: ab
    1 Tokens: ab

    Please enter a line: a=b
    2 Tokens: a,b

    Please enter a line: a-
    1 Tokens: a

    Please enter a line: a-=
    1 Tokens: a

    Please enter a line: =a-
    1 Tokens: a

    Please enter a line: a=-b
    2 Tokens: a,b

    Please enter a line: a--b-
    2 Tokens: a,b

    Please enter a line: -a==b-c==
    3 Tokens: a,b,c

## See also

`split`

## Name

triangle — draw a triangle

## Synopsis

    open window 100,100
    triangle 100,100,50,50,100,50
    fill triangle 50,100,100,50,200,200
    clear fill triangle 20,20,10,10,200,200

## Description

The `triangle`-command draws a triangle; it requires 6 parameters: The x- and y-coordinates of the three points making up the triangle. With the optional keywords `clear` and `fill` (which may appear both and in any sequence) the triangle can be cleared and filled respectively.

## Example

    open window 200,200
    do
      phi=phi+0.2
      i=i+2
      color mod(i,255),mod(85+2*i,255),mod(170+3*i,255)
      dx=100*sin(phi):dy=20*cos(phi)
      fill triangle 100+20*sin(phi),100+20*cos(phi),100-20*sin(phi),100-20*cos(phi),100-80*cos(phi),100+80*sin(phi)
      sleep 0.1
    loop

This example draws a colored triangles until you get exhausted.

## See also

`open window`, `open printer`, `line`, `circle``, rectangle`

## Name

trim$() — remove leading and trailing spaces from its argument

## Synopsis

    a$=trim$(b$)

## Description

The `trim$`-function removes all whitespaces from the left and from the right end of a string and returns the result. Calling `trim$` is equivalent to calling `rtrim$(ltrim$())`.

## Example

    do
      input "Continue ? Please answer yes or no: " a$
      a$=lower$(trim$(a$))
      if (len(a$)>0 and a$=left$("no",len(a$)) exit
    loop

This example asks for an answer (`yes` or `no`) and removes spaces with `trim$` to make the comparison with the string `"no"` more bulletproof.

## See also

`ltrim$`, `rtrim$`

## Name

true — a constant with the value of 1

## Synopsis

    okay=true

## Description

The constant `true` can be assigned to variables which will later appear in conditions (e.g. an `if`-statement.

`true` may also be written as `TRUE` or even `TrUe`.

## Example

    input "Please enter a string of all upper letters: " a$
    if (is_upper(a$)) print "Okay"

    sub is_upper(a$)
      if (a$=upper$(a$)) return true
      return false
    end sub

## See also

`false`

### U

## Name

until — end a `repeat`-loop

## Synopsis

    repeat
      …
    until (…)

## Description

The `until`-keyword ends a loop, which has been introduced by the `repeat`-keyword. `until` requires a condition in braces (or an expression, see here for details) as an argument; the loop will continue until this condition evaluates to true.

## Example

    c=1
    s=1
    repeat
      l=c
      s=-(s+sig(s))
      c=c+1/s
      print c
    until(abs(l-c)<0.000001)

This program calculates the sequence 1/1-1/2+1/3-1/4+1/5-1/6+1/7-1/8+ … ; please let me know, if you know against which value this converges.

## See also

`repeat`

## Name

upper$() — convert a string to upper case

## Synopsis

    u$=upper$(a$)

## Description

The `upper$`-function accepts a single string argument and converts it to all upper case.

## Example

    line input "Please enter a sentence without the letter 'e': " l$
    p=instr(upper$(l$),"E")
    if (p) then
      l$=lower$(l$)
      mid$(l$,p,1)="E"
      print "Hey, you are wrong, see here!"
      print l$
    else
      print "Thanks."
    endif

This program asks for a sentence and marks the first (if any) occurrence of the letter 'e' by coverting it to upper case (in contrast to the rest of the sentence, which is converted to lower case).

## See also

`lower$`

## Name

using — Specify the format for printing a number

## Synopsis

    print a using "##.###"
    print a using("##.###",",.")

## Description

The `using`-keyword may appear as part of the `print`-statement and specifies the format (e.g. the number of digits before and after the decimal dot), which should be used to print the number.

The possible values for the format argument (`"##.###"` in the synopsis above) are described within the entry for the `str$`-function; especially the second line in the synopsis (`print a using("##.###",",.")`) will become clear after referring to `str$`. In fact the `using` clause is closely related to the `str$`-function; the former can always be rewritten using the latter; i.e. `print foo using bar$` is always equivalent to `print str$(foo,bar$)`. Therefore you should check out `str$` to learn more.

## Example

    for a=1 to 10
      print sqrt(ran(10000*a)) using "#########.#####"
    next a

This example prints a column of square roots of random number, nicely aligned at the decimal dot.

## See also

`print`, `str$`

### V

## Name

val() — converts a string to a number

## Synopsis

    x=val(x$)

## Description

The `val`-function checks, if the start of its string argument forms a floating point number and then returns this number. The string therefore has to start with digits (only whitespace in front is allowed), otherwise the `val`-function returns zero.

## Example

    input "Please enter a length, either in inches (in) or centimeters (cm) " l$
    if (right$(l$,2)="in") then
      l=val(l$)*2.51
    else
      l=val(l$)
    print "You have entered ",l,"cm."

This example queries for a length and checks, if it has been specified in inches or centimeters. The length is then converted to centimeters.

## See also

`str$`

### W

## Name

wait — pause, sleep, wait for the specified number of seconds

## Synopsis

    wait 4

## Description

The `wait`-command has many different names: You may write `pause`, `sleep` or `wait` interchangeably; whatever you write, yabasic will always do exactly the same.

Therefore you should refer to the entry for the `pause`-function for further information.

## Name

wend — end a `while`-loop

## Synopsis

    while(a<b)
      …
    wend

## Description

The `wend`-keyword marks the end of a `while`-loop. Please see the `while`-keyword for more details.

`wend` can be written as `end while` or even `end-while`.

## Example

    line input "Please enter a sentence: " a$
    p=instr(a$,"e")
    while(p)
      mid$(a$,p,1)="E"
      p=instr(a$,"e")
    wend
    print a$

This example reads a sentence and converts every occurrence of the letter `e` into uppercase (`E`).

## See also

`while` (which is just the following entry).

## Name

while — start a `while`-loop

## Synopsis

    while(…)
      …
    wend

## Description

The `while`-keyword starts a `while`-loop, i.e. a loop that is executed as long as the condition (which is specified in braces after the keyword `while`) evaluates to `true`.

Note, that the body of such a `while`-loop will not be executed at all, if the condition following the `while`-keyword is not true initially.

If you want to leave the loop prematurely, you may use the `break`-statement.

## Example

    open #1,"foo"
    while(!eof(1))
      line input #1 a$
      print a$
    wend

This program reads the file `foo` and prints it line by line.

## See also

`until`, `break`, `wend`, `do`

## Name

origin — move the origin of a window

## Synopsis

    open window 200,200
    origin "cc"

## Description

The `origin`-command applies to graphic windows and moves the origin of the coordinate system to one of nine point within the window. The normal position of the origin is in the upper left corner of the window; however in some cases this is inconvenient and moving the origin may save you from subtracting a constant offset from all of your coordinates.

However, you may not move the origin to an arbitrary position; in horizontal position there are only three positions: left, center and right, which are decoded by the letters `l`, `c` and `r`. In vertical position the allowed positions are top, center and bottom; encoded by the letters `t`, `c` and `b`. Taking the letters together, you arrive at a string, which might be passed as an argument to the command; e.g. `"cc"` or `"rt"`.

## Example

100,100

    open window 200,200
    window origin "cc"
    circle 0,0,60

This example draws a circle, centered at the center of the window.

## See also

`open window`

### X

## Name

xor() — compute the exclusive or

## Synopsis

    x=xor(a,b)

## Description

The `xor` computes the bitwise exclusive or of its two numeric arguments. To understand the result, both arguments should be viewed as binary numbers (i.e. a series of 0 and 1); a bit of the result will then be 1, if exactly one argument has a 1 and the other has a 0 at this position in their binary representation.

Note, that both arguments are silently converted to integer values and that negative numbers have their own binary representation and may lead to unexpected results when passed to `and`.

## Example

    print xor(7,4)

This will print `3`. This result is obvious, if you note, that the binary representation of 7 and 4 are 111 and 100 respectively; this will yield 011 in binary representation or 2 as decimal.

The `eor`-function is the same as the `xor` function; both are synonymous; however they have each their own description, so you may check out the entry of `eor` for a slightly different view.

## See also

`and`, `or`, `eor`, `not`

### Special characters

## Name

# — either a comment or a marker for a file-number

## Synopsis

    # This is a comment, but the line below not !
    open #1,"foo"

## Description

The hash ('`#`') has two totally unrelated uses:

- A hash might appear in commands related with file-io. yabasic uses simple numbers to refer to open files (within `input`, `print`, `peek` or `eof`). In those commands the hash may precede the number, which species the file. Please see those commands for further information and examples; the rest of this entry is about the second use (as a comment).

- As the very first character within a line, a hash introduces comments (similar to `rem`).

'`#`' as a comment is common in most scripting languages and has a special use under Unix: If the very first line of any Unix-program begins with the character sequence '`#!`' ("she-bang", no spaces allowed), the rest of the line is taken as the program that should be used to execute the script. I.e. if your yabasic-program starts with '`#!/usr/local/bin/yabasic`', the program `/usr/local/bin/yabasic` will be invoked to execute the rest of the program. As a remark for windows-users: This mechanism ensures, that yabasic will be invoked to execute your program; the ending of the file (e.g. `.yab`) will be ignored by Unix.

## Example

    # This line is a valid comment
    print "Hello " : # But this is a syntax error, because
    print "World!" : # the hash is not the first character !

Note, that this example will produce a syntax error and is not a valid program !

## See also

`input`, `print`, `peek` or `eof`, `//`, `rem`

## Name

// — starts a comment

## Synopsis

    //  This is a comment !

## Description

The double-slash ('`//`') is (besides `REM` and '`#`') the third way to start a comment. '`//`' is the latest and greatest in the field of commenting and allows yabasic to catch up with such cool languages like C++ and Java.

## Example

    // Another comment.
    print "Hello world !" // Another comment

Unlike the example given for '`#`' this example is syntactically correct and will not produce an error.

## See also

`#`, `rem`

## Name

@ — synonymous to `at`

## Synopsis

    clear screen
    …
    print @(a,b)

## Description

As '`@`' is simply a synonym for `at`, please see `at` for further information.

## See also

`at`

## Name

: — separate commands from each other

## Synopsis

    print "Hello ":print "World"

## Description

The colon ('`:`') separates multiple commands on a single line.

The colon and the newline-character have mostly the same effect, only that the latter, well, starts a new line too. The only other difference is their effect within the (so-called) short `if`, which is an `if`-statement without the keyword `then`. Please see the entry for `if` for more details.

## Example

    if (a<10) print "Hello ":print "World !"

This example demonstrates the difference between colon and newline as described above.

## See also

`if`

## Name

; — suppress the implicit newline after a `print`-statement

## Synopsis

    print "foo",bar;

## Description

The semicolon ('`;`') may only appear at the last position within a `print`-statement. It suppresses the implicit newline, which yabasic normally adds after each `print`-statement.

Put another way: Normally the output of each `print`-statement appears on a line by itself. If you rather want the output of many `print`-statements to appear on a single line, you should end the `print`-statement with a semicolon.

## Example

    print "Hello ";:print "World !"

This example prints `Hello World !` in a single line.

## See also

`print`

## Name

** or ^ — raise its first argument to the power of its second

## Synopsis

    print 2**b
    print 3^4

## Description

`**` (or `^`, which is an exact synonym), is the arithmetic operator of exponentiation; it requires one number to its left and a second one to its right; `**` then raises the first argument to the power of the second and returns the result. The result will only be computed if it yields a real number (as opposed to a complex number); this means, that the power can not be computed, if the first argument is negative and the second one is fractional. On the other hand, the second argument can be fractional, if the first one ist positive; this means, that `**` may be used to compute arbitrary roots: e.g. `x**0.5` computes the square root of `x`.

## Example

    print 2**0.5

## See also

`sqrt`

### Reserved Words

Here is a list of all reserved words in yabasic. Please make sure, that you do not try to use one of them as the name of a variable or subroutine. Or, the other way around: If you get some mysterious error from yabasic and you just can't figure out why, then you might be using one of the reserved words below, without knowing.

Anyway, here is the list:

`ABS` | `ACOS` | `AND` | `ARRAYDIM` | `ARRAYDIMENSION`
`ARRAYSIZE` | `AS` | `ASC` | `ASIN` | `AT`
`ATAN` | `BEEP` | `BELL` | `BIN$` | `BIND`
`BITBLIT` | `BITBLIT$` | `BITBLT` | `BITBLT$` | `BOX`
`BREAK` | `CASE` | `CHR$` | `CIRCLE` | `CLEAR`
`CLOSE` | `COLOR` | `COLOUR` | `COMPILE` | `CONTINUE`
`COS` | `CURVE` | `DATA` | `DATE$` | `DEC`
`DEFAULT` | `DIM` | `DO` | `DOT` | `ELSE`
`ELSEIF` | `ELSIF` | `END` | `ENDIF` | `EOF`
`EOR` | `ERROR` | `EXECUTE` | `EXECUTE$` | `EXIT`
`EXP` | `EXPORT` | `FI` | `FILL` | `FILLED`
`FOR` | `FRAC` | `GETBIT$` | `GETSCREEN$` | `GLOB`
`GOSUB` | `GOTO` | `HEX$` | `IF` | `INKEY$`
`INPUT` | `INSTR` | `INT` | `INTERRUPT` | `LABEL`
`LEFT$` | `LEN` | `LET` | `LINE` | `LOCAL`
`LOG` | `LOOP` | `LOWER$` | `LTRIM$` | `MAX`
`MID$` | `MIN` | `MOD` | `MOUSEB` | `MOUSEBUTTON`
`MOUSEMOD` | `MOUSEMODIFIER` | `MOUSEX` | `MOUSEY` | `NEW`
`NEXT` | `NOT` | `NUMPARAM` | `ON` | `OPEN`
`OR` | `ORIGIN` | `PAUSE` | `PEEK` | `PEEK$`
`POKE` | `PRINT` | `PRINTER` | `PUTBIT` | `PUTSCREEN`
`RAN` | `READ` | `READING` | `RECT` | `RECTANGLE`
`REDIM` | `REPEAT` | `RESTORE` | `RETURN` | `REVERSE`
`RIGHT$` | `RINSTR` | `RTRIM$` | `SCREEN` | `SEEK`
`SIG` | `SIN` | `SLEEP` | `SPLIT` | `SPLIT$`
`SQR` | `SQRT` | `STATIC` | `STEP` | `STR$`
`SUB` | `SUBROUTINE` | `SWITCH` | `SYSTEM` | `SYSTEM$`
`TAN` | `TELL` | `TEXT` | `THEN` | `TIME$`
`TO` | `TOKEN` | `TOKEN$` | `TRIANGLE` | `TRIM$`
`UNTIL` | `UPPER$` | `USING` | `VAL` | `WAIT`
`WEND` | `WHILE` | `WINDOW` | `WRITING` | `XOR`

Please see here for explanations on how to use these words in yabasic.

## Chapter 7. A grab-bag of some general concepts and terms

This chapter presents some general concepts and terms, which deserve a description on their own, but are not associated with a single command or function in yabasic. Most of these topics do not lend themselves to be read alone, rather they might be read (or skimmed) as background material if an entry from the alphabetical list of commands refers to them.

### Logical shortcuts

Logical shortcuts are no special language construct and there is no keyword for them; they are just a way to evaluate logical expressions. Logical expressions (i.e. a series of conditions or comparisons joined by `and` or `or`) are only evaluated until the final result of the expression can be determined. An example:

    if (a<>0 and b/a>2) print "b is at least twice as big as a"

The logical expression `a<>0 and b/a>2` consists of two comparisons, both of which must be true, if the `print` statement should be executed. Now, if the first comparison (`a<>0`) is `false`, the whole logical expression can never be `true` and the second comparison (`b/a>2`) need not be evaluated.

This is exactly, how yabasic behaves: The evaluation of a composed logical expressions is terminated immediately, as soon as the final result can be deduced from the already evaluated parts.

In practice, this has the following consequences:

- If two or more comparisons are joined with `and` and one comparison results in `false`, the logical expression is evaluated no further and the overall result is `false`.

- If two or more comparisons are joined with `or` and one comparison results in `true`, the logical expression is evaluated no further and the result is `true`.

“Nice, but whats this good for ?”, I hear you say. Well, just have another look at the example, especially the second comparison (`b/a>2`); dividing `b` by `a` is potentially hazardous: If `a` equals zero, the expression will cause an error and your program will terminate. To avoid this, the first part of the comparison (`a<>0`) checks, if the second one can be evaluated without risk. This pre-checking is the most common usage and primary motivation for logical shortcuts (and the reason why most programming languages implement them).

### Conditions and expressions

Well, bottomline there is no difference or distinction between conditions and expressions, at least as yabasic is concerned. So you may assign the result of comparisons to variables or use an arithmetic expression or a simple variable within a condition (e.g. within an `if`-statement). So the constructs shown in the example below are all totally valid:

    input "Please enter a number between 1 and 10: " a

    rem   Assigning the result of a comparison to a variable
    okay=a>=1 and a<=10

    rem   Use a variable within an if-statement
    if (not okay) error "Wrong, wrong !"

So conditions and expressions are really the same thing (at least as long as yabasic is concerned). Therefore the terms conditions and expression can really be used interchangeably, at least in theory. In reality the term condition is used in connection with `if` or `while` whereas the term expression tends to be used more often within arithmetic context.

### References on arrays

References on arrays are the only way to refer to an array as a whole and to pass it to subroutines or functions like `arraydim` or `arraysize`. Whereas (for example) `a(2)` designates the second element of the array `a`, `a()` (with empty braces) refers to the array `a` itself. `a()` is called an array reference.

If you pass an array reference to one of your own subroutines, you need to be aware, that the subroutine will be able to modify the array you have passed in. So passing an array reference does not create a copy of the array; this has some interesting consequences:

- Speed and space: Creating a copy of an array would be a time (and resource) consuming operation; passing just a reference is cheap and fast.

- Returning many values: A subroutine, that wants to give back more than one value, may require an array reference among its arguments and then store its many return values within this array. This is the only way to return more than one value from a subroutine.

### Specifying Filenames under Windows

As you probably know, windows uses the character '`\`' to separate the directories within a pathname; an example would be `C:\yabasic\yabasic.exe` (the usual location of the yabasic executable). However, the very same character '`\`' is used to construct escape sequences, not only in yabasic but in most other programming languages.

Therefore the string `"C:\t.dat"` does not specify the file `t.dat` within the directory `C:`; this is because the sequence '`\t`' is translated into the tab-character. To specify this filename, you need to use the string `"C:\\t.dat"` (note the double slash '`\\`').

### Escape-sequences

Escape-sequences are the preferred way of specifying 'special' characters. They are introduced by the '\'-character and followed by one of a few regular letters, e.g. '\n' or '\r' (see the table below).

Escape-sequences may occur within any string at any position; they are replaced at parsetime (opposed to runtime), i.e. as soon as yabasic discovers the string, with their corresponding special character. As a consequence of this `len("\a")` returns 1, because yabasic replaces `"\a"` with the matching special character just before the program executes.

Table 7.1. Escape sequences

Escape Sequence | Matching special character
--- | ---
`\n` | newline
`\t` | tabulator
`\v` | vertical tabulator
`\b` | backspace
`\r` | carriage return
`\f` | formfeed
`\a` | alert (i.e. a beeping sound)
`\\` | backslash
`\'` | single quote
`\"` | double quote
`\x`HEX | `chr$(`HEX`)` (see below)

Note, that an escape sequences of the form \xHEX allows to encode arbitrary characters as long as you know their position (as a hex-number) within the ascii-charset: For example \x012 is transformed into the character `chr$(18)` (or `chr$(dec("12",16))`. Note that \x requires a hexa-decimal number (and the hexa-decimal string "12" corresponds to the decimal number 18).

### Creating a standalone program from your yabasic-program

### Note

The `bind`-feature, which is described below, is at an experimental stage right now. It works (at least for me !) under Windows and Linux, but I cannot even promise it for other variants of Unix. However, if it does not work for your Unix, I will at least try to make it work, if you give me sufficient information of your system.

Sometimes you may want to give one of your yabasic-programs to other people. However, what if those other people do not have yabasic installed ? In that case you may create a standalone-program from your yabasic-program, i.e. an executable, that may be executed on its own, standalone, even (and especially !) on computers, that do not have yabasic installed. Having created a standalone program, you may pass it around like any other program (e.g. one written in C) and you can be sure that your program will execute right away.

Such a standalone-program is simply created by copying the full yabasic-interpreter and your yabasic-program (plus all the libraries it does `import`) together into a single, new program, whose name might be chosen at will (under windows of course it should have the ending `.exe`). If you decide to create a standalone-program, there are three bits in yabasic, that you may use:

- The `bind`-command, which does the actual job of creating the standalone program from the yabasic-interpreter and your program.

- The command-line Option `-bind` (available under windows and Unix), which does the same from the command-line.

- The special `peek("isbound")`, which may be used to check, if the yabasic-program containing this `peek` is bound to the interpreter as part of a standalone program.

With these bits you know enough to create a standalone-program. Actually there are two ways to do this: on the commandline and from within your program.

#### Creating a standalone-program from the commandline

Let's say you have the following very simple program within the file `foo.yab`:

    print "Hello World !"

Normally you would start this yabasic-program by typing `yabasic foo.yab` and as a result the string `Hello World !` would appear on your screen. However, to create a standalone-program from `foo.yab` you would type:

`yabasic -bind foo.exe foo.yab`

This command does not execute your program `foo.yab` but rather create a standalone-program `foo.exe`. Note: under Unix you would probably name the standalone program `foo` or such, omitting the windows-specific ending `.exe`.

Yabasic will confirm by printing something like: `---Info: Successfully bound 'yabasic' and 'foo.yab' into 'foo.exe'`.

After that you will find a program `foo.exe` (which must be made executable with the chmod-command under Unix first). Now, executing this program `foo.exe` (or `foo` under Unix) will produce the output `Hello World !`.

This newly created program `foo.exe` might be passed around to anyone, even if he does not have yabasic installed.

#### Creating a standalone-program from within your program

It is possible to write a yabasic-program, that binds itself to the yabasic-interpreter. Here is an example:

    if (!peek("isbound")) then
      bind "foo"
      print "Successfully created the standalone executable 'foo' !"
      exit
    endif

    print "Hello World !"

If you run this program (which may be saved in the file `foo.yab`) via `yabasic foo.yab`, the `peek("isbound")` in the first line will check, if the program is already part of a standalone-program. If not (i.e. if the yabasic-interpreter and the yabasic-program are separate files) the `bind`-command will create a standalone program `foo` containing both. As a result you would see the output `Successfully created the standalone executable 'foo' !`. Note: Under Windows you would probably choose the filename `foo.exe`.

Now, if you run this standalone executable `foo` (or `foo.exe`), the very same yabasic-program that is shown above will be executed again. However, this time the `peek("isbound")` will return `TRUE` and therefore the condition of the `if`-statement is false and the three lines after `then` are not executed. Rather the last `print`-statement will run, and you will see the output `Hello World !`.

That way a yabasic-program may turn itself into a standalone-program.

#### Downsides of creating a standalone program

Now, before you go out and turn all your yabasic-programs into standalone programs, please take a second to consider the downsides of doing so:

- The new standalone program will be at least as big as the interpreter itself, so you need to pass a few hundred kilobytes around, just to save people from having to install yabasic themselves.

- There is no easy way to extract your yabasic-program from within the standalone program: If you ever want to change it, you need to have it around separately.

- If a new version of yabasic becomes available, again you need to recreate all of your standalone programs to take advantage of bugfixes and improvements.

So, being able to create a standalone program is certainly a good thing, but certainly not a silver bullet.

#### See also

The `bind`-command, the `peek`-function and the commandline options for Unix and Windows.

## Chapter 8. A few example programs

## A very simple program

The program below is a very simple program:

    repeat
      input "Please enter the first number, to add " a
      input "Please enter the second number, to add " b
      print a+b
    until(a=0 and b=0)

This program requests two numbers, which it than adds. The process is repeated until you enter zero (or nothing) twice.

## The demo of yabasic

The listing below is the demo of yabasic. Note, that parts of this demo have been written before some of the more advanced features (e.g subroutines) of yabasic have been implemented. So please do not take this as a particular good example of yabasic-code.

    //
    //      This program demos yabasic
    //

    //      Check, if screen is large enough
    clear screen
    sw=peek("screenwidth"):sh=peek("screenheight")
    if (sw<78 or sh<24) then
      print
      print "  Sorry, but your screen is to small to run this demo !"
      print
      end
    endif
    sw=78:sh=24

    //  Initialize everything
    restore mmdata
    read mmnum:dim mmtext$(mmnum)
    for a=1 to mmnum:read mmtext$(a):next a

    //  Main loop selection of demo
    ysel=1
    label mainloop
    clear screen
    print colour("cyan","magenta") at(7,2) "################################"
    print colour("cyan","magenta") at(7,3) "################################"
    print colour("cyan","magenta") at(7,4) "################################"
    print colour("yellow","blue") at(8,3) " This is the demo for yabasic "
    yoff=7
    for a=1 to mmnum
      if (a=mmnum) then ydisp=1:else ydisp=0:fi
      if (a=ysel) then
        print colour("blue","green") at(5,yoff+ydisp+a) mmtext$(a);
      else
        print at(5,yoff+ydisp+a) mmtext$(a);
      endif
    next a
    print at(3,sh-3) "Move selection with CURSOR KEYS (or u and d),"
    print at(3,sh-2) "Press RETURN or SPACE to choose, ESC to quit."

    do    // loop for keys pressed
      rev=1
      do    // loop for blinking
        k$=inkey$(0.4)
        if (k$="") then
          if (ysel=mmnum) then
            if (rev=1) then
              print colour("blue","green") at(5,yoff+mmnum+1) mmtext$(mmnum);
              rev=0
            else
              print colour("yellow","red") at(5,yoff+mmnum+1) mmtext$(mmnum);
              rev=1
            endif
          endif
        else    // key has been pressed, leave loop
          break
        endif
      loop    // loop for blinking

      yalt=ysel
      if (k$="up" or k$="u") then
        if (ysel=1) then ysel=mmnum else ysel=ysel-1 fi
        redraw():heal():continue
      fi
      if (k$="down" or k$="d") then
        if (ysel=mmnum) then ysel=1 else ysel=ysel+1 fi
        redraw():heal():continue
      fi
      if (k$=" " or k$="enter" or k$="right") then
        on ysel gosub overview,bitmap,tetraeder,endit
        goto mainloop
      fi
      if (k$="esc") then
        endit()
      fi
      beep
      print at(3,sh-5) "Invalid key: ",k$,"         "
    loop    // loop for keys pressed

    //  redraw line
    sub redraw()
      if (yalt=mmnum) then ydisp=1:else ydisp=0:fi
      print at(5,yoff+yalt+ydisp) mmtext$(yalt);
      if (ysel=mmnum) then ydisp=1:else ydisp=0:fi
      print colour("blue","green") at(5,yoff+ysel+ydisp) mmtext$(ysel);
      return
    end sub

    //  erase a line
    sub heal()
      print at(3,sh-5) "                                                       "
      return
    end sub

    //  Go here to exit
    label endit
      print at(3,sh-8) "Hope you liked it ...\n   ";
      exit
    return

    //  Present a short overview
    label overview
      clear screen
      print
      print "  Yabasic is a quite traditional basic: It comes with"
      print "  print, input, for-next-loops, goto, gosub, while and"
      print "  repeat. It has user defined procedures and libraries,"
      print "  however, it is not object oriented.\n"
      print "  Yabasic makes it easy to open a window, draw lines"
      print "  and print the resulting picture.\n"
      print "  Yabasic programs are interpreted and run under Unix"
      print "  and Windows. The Yabasic interpreter (around 200K)"
      print "  and any Yabasic program can be glued together to"
      print "  form a standalone executable.\n"
      print "  Yabasic is free software, i.e. subject to the"
      print "  GNU copyright.\n"
      print "\n\n\n  While you read this, I am calculating prime numbers,\n"
      print "  Press any key to return to main menu ..."
      can=1
      print at(6,17) "This is a prime number: "
      label nextcan
      can=can+2
      for i=2 to sqrt(can):if (frac(can/i)=0) then goto notprime:fi:next i
      print at(32,17) can;
      label notprime
      if (lower$(inkey$(0))<>"") then
        print at(10,sh) "Wrapping around once ...";
        for x=1 to sw
          a$=getscreen$(0,0,1,sh-2)
          b$=getscreen$(1,0,sw-1,sh-2)
          putscreen b$,0,0
          putscreen a$,sw-1,0
        next x
        sleep 2
        return
      fi
    goto nextcan

    //  Show some animated bitmaps
    label bitmap
      clear screen
      print
      print "Yabasic offers some commands for drawing simple graphics."
      print reverse at(5,12) " Press any key to return to main menu ... "

      n=20
      open window 400,400

      for b=20 to 0 step -1
        color 255-b*12,0,b*12
        fill circle 200,200,b
      next b
      c$=getbit$(179,179,221,221)
      for a=1 to 2000
        color ran(255),ran(255),ran(255)
        x=ran(500)-100:y=ran(500)-100
        fill rectangle ran(500)-100,ran(500)-100,ran(500)-100,ran(500)-100
      next a

      x=200:y=200:phi=ran(2*pi):dx=2*sin(phi):dy=2*cos(phi)
      o$=""
      count=0
      label pong
        count=count+1
        if (o$<>"") putbit o$,xo-2,yo-2
        if (count>1000) then
          phi=ran(2*pi):dx=2*sin(phi):dy=2*cos(phi)
          sleep 2
          count=0
        endif
        xo=x:yo=y
        x=x+dx:y=y+dy
        o$=getbit$(x-2,y-2,x+46,y+46)
        putbit c$,x,y,"t"
        if (x<0 or x>360) dx=-dx
        if (y<0 or y>360) dy=-dy
        if (inkey$(0)<>"") then
          close window
          return
        endif
      goto pong
    return

    label tetraeder

    open window 400,400
    clear window
    clear screen
    print reverse at(5,12) " Press any key to return to main menu ... "

    dim opoints(4,3)
    restore points
    for n=1 to 4:for p=1 to 3:read opoints(n,p):next p:next n

    dim triangles(4,3)
    restore triangles
    for n=1 to 4:for p=1 to 3:read triangles(n,p):next p:next n

    phi=0:dphi=0.1:psi=0:dpsi=0.05
    dim points(4,3)

    r=60:g=20
    dr=0.5:dg=1.2:db=3
    label main

      phi=phi+dphi
      psi=psi+dpsi
      for n=1 to 4
        points(n,1)=opoints(n,1)*cos(phi)-opoints(n,2)*sin(phi)
        points(n,2)=opoints(n,2)*cos(phi)+opoints(n,1)*sin(phi)
        p2=          points(n,2)*cos(psi)-opoints(n,3)*sin(psi)
        points(n,3)=opoints(n,3)*cos(psi)+ points(n,2)*sin(psi)
        points(n,2)=p2
      next n

      r=r+dr:if (r<0 or r>60) dr=-dr
      g=g+dg:if (g<0 or g>60) dg=-dg
      b=b+db:if (b<0 or b>60) db=-db
      dm=dm+0.01
      m=120-80*sin(dm)
      for n=1 to 4
        p1=triangles(n,1)
        p2=triangles(n,2)
        p3=triangles(n,3)
        n1=points(p1,1)+points(p2,1)+points(p3,1)
        n2=points(p1,2)+points(p2,2)+points(p3,2)
        n3=points(p1,3)+points(p2,3)+points(p3,3)
        if (n3>0) then
          sp=n1*0.5-n2*0.7-n3*0.6
          color 60+r+30*sp,60+g+30*sp,60+b+30*sp
          fill triangle 200+m*points(p1,1),200+m*points(p1,2),200+m*points(p2,1),200+m*points(p2,2),200+m*points(p3,1),200+m*points(p3,2)
        endif
      next n
      if (inkey$(0.1)<>"") close window:return
      clear window
    goto main

    label points
    data  -1,-1,+1,  +1,-1,-1,  +1,+1,+1,  -1,+1,-1
    label triangles
    data  1,2,4,  2,3,4,  1,3,4,  1,2,3

    //  Data section ...
    label mmdata
    //  Data for main menu: Number and text of entries in main menu
    data 4
    data "   Yabasic in a nutshell   "
    data "   Some graphics           "
    data "   A rotating Tetraeder    "
    data "   Exit this demo          "

## Chapter 9. The Copyright of yabasic

yabasic may be copied only under the terms of the Artistic License or the GNU General Public License (GPL), both of which are distributed with yabasic.

[Can't you make up your mind ?!], I hear you say. Umm, well yes. In fact I do not want to read or try to understand them both, so I have put the burden on you (grin). However, I think that the Artistic License is more liberal and gives you more rights and you should choose it; on the other hand the GPL is more widely known and a lot of software is distributed under its terms.

Here is a list of things that are possible under the terms of the Artistic License:

- Put yabasic on your own homepage or CD and even charge for the service of distributing yabasic.

- Write your own yabasic-programs, pack your program and yabasic into a package and sell the whole thing.

- Modify yabasic and add or remove features, sell the modified version.