====== Syntax ======

An **XC=BASIC** program is built from one or more plain ASCII text files that consist of lines, allowing one or more statements per line.

Each line may optionally contain a label and zero or more statements separated by a colon ('':''):

  label1: print "hello world"
  label2:
  print "hello again"
  let x = 5 : print x : rem "these were more statements in a line"
===== Whitespace =====

Whitespace (tabs, spaces, empty lines) is ignored. Indentation is allowed and encouraged.

  rem ** fibonacci series **
  let max = 32767
  let t1 = 0
  let t2 = 1
  print "fibonacci series:"
  loop:
    print t1, " "
    let nx = t1 + t2
    let t1 = t2
    let t2 = nx
    if nx < max then goto loop
  end
  
Whitespace is not required between keywords and identifiers, though it's recommended for readability. The following is a valid statement:

  forindex=0to255

===== Multi-line statements  =====

Line break is ignored if the last character of a line is a tilde (''~'') character. This can be useful in a ''DATA'' statement with a long list, for example:

  data my_long_data[] = 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, ~
                        11, 12, 13, 14, 15

Note that no other character is allowed after the tilde, including whitespace.

===== Case sensitivity =====

Keywords may be written in lowercase or uppercase as well. All identifiers (variable names, procedure names, etc.) can be mixed-case and are case sensitive by default.

If the ''civars'' [[compiler_options|compiler option]] is turned on, variable names are treated insensitive. This only applies to variable names. Labels and other identifiers are case sensitive.

===== Identifiers =====

Identifiers can be of any length, may contain mixed-case alphanumeric characters and underscores, though they may not start with a number, nor with a keyword.

Valid identifiers include:

  a
  A
  _myVar
  myVar2
  
The following are not valid identifiers:

  remark
  2pac
  letter

===== Includes =====

The ''[[INCLUDE|INCLUDE]]'' directive is useful in splitting your program to several files.

===== Comments  =====

The only way to add comments is the [[REM|REM]] statement. The ''REM'' keyword however has two aliases: the semicolon ('';'') and the single quote (''''').

    rem This is a comment
    ' This is also a comment
    ; This is also a comment

===== String literals =====

Strings are enclosed in double quotes (''"''). All characters in strings will be translated from ASCII to PETSCII (or screencodes - depending on the context).

There are several escape sequences that you can use in string literals to be able to print special PETSCII characters.

The escape sequence ''{num}'' (where ''num'' is a decimal number) will be replaced by the PETSCII code indicated by ''num''.
You can also use the following convenience escape sequences: ''{CLR}'', ''{HOME}'', ''{INSERT}'', ''{DEL}'', ''{CR}'', ''{REV_ON}'', ''{REV_OFF}'', ''{CRSR_UP}'', ''{CRSR_DOWN}'', ''{CRSR_LEFT}'', ''{CRSR_RIGHT}''

Example:

  print "{CLR}welcome to a fresh new screen"
  print "this is line one{CR}and this is line two"
  print "{5}white text"
  
Make sure to check the list of all [[petscii_escape_sequences|]].
===== Character literals =====

Since version 1.2, a character enclosed in single quotes (''''') evaluates to its PETSCII code.  Escape sequences are supported in character literals as well.

Example:

  print 'a' + 1
  rem -- will output: 66
  print '{white}'
  rem -- will output: 5