Difference between revisions of "Variable"

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<center>'''Variable names'''</center>
 
<center>'''Variable names'''</center>
Variables in QB64 can be any name except the names of keywords and may not contain spaces or non-alphabetical/non-numerical characters (except "." and "_"), if numerical characters are used in the name at least one alphabetical character has to be used before the numerical character, the same applies to ".", in case a "." is used in the name at least one character has to follow the "." (numerical or alphabetical).
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Variables in QB64 can be any name except the names of QB64 or Qbasic keywords and may not contain spaces or non-alphabetical/non-numerical characters (except "." and "_"). Numerical characters cannot be used as the first character of a variable or array name!
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[[Arrays]] variable names can hold many values in one variable name by specifying a reference index enclosed in paranteses.
  
  
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Groups of variable names can be type defined by the first letter or list of letters of the names using [[DEFINT]], [[DEFLNG]], [[DEFSNG]], [[DEFDBL]], [[DEFSTR]] or [[_DEFINE]] [[AS]] in QB64.
 
Groups of variable names can be type defined by the first letter or list of letters of the names using [[DEFINT]], [[DEFLNG]], [[DEFSNG]], [[DEFDBL]], [[DEFSTR]] or [[_DEFINE]] [[AS]] in QB64.
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[[$DYNAMIC]] arrays can be resized and can retain their remaining element values when used with [[_PRESERVE]] in QB64.
  
  
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[[STATIC]] sub-procedure values keep their value after the procedure is exited. They will hold an empty value when first used.
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[[STATIC]] sub-procedure values keep their value after the sub-procedure is exited. They will hold an empty value when first used.
  
  
 
Variables are used to hold program data information that is attained through the program flow, either by user input, calculations or by other ways of communicaton (as with I/O, memory, TCP/IP or files).
 
Variables are used to hold program data information that is attained through the program flow, either by user input, calculations or by other ways of communicaton (as with I/O, memory, TCP/IP or files).
 
  
  
 
Assignment of variable values can be done using the = assignment symbol (variable1.number = 500, for example).
 
Assignment of variable values can be done using the = assignment symbol (variable1.number = 500, for example).
 
 
[[Arrays]] is a special usage of variables that can hold many values in one variable name by specifying a reference index enclosed in paranteses.
 
 
 
  
  

Revision as of 19:17, 15 August 2011

A variable is a "container" name that can hold a numerical or string value which can be referenced or changed by the program (as opposed to CONSTant values which never change).


Variable names

Variables in QB64 can be any name except the names of QB64 or Qbasic keywords and may not contain spaces or non-alphabetical/non-numerical characters (except "." and "_"). Numerical characters cannot be used as the first character of a variable or array name!


Arrays variable names can hold many values in one variable name by specifying a reference index enclosed in paranteses.


Variable types

Variables can be defined as a specific type using a variable type suffix or by using a DIM or REDIM(for dynamic arrays only) statement AS a variable type of _BIT, _BYTE, INTEGER, LONG, SINGLE, DOUBLE, _INTEGER64, _FLOAT or STRING in QB64.


Groups of variable names can be type defined by the first letter or list of letters of the names using DEFINT, DEFLNG, DEFSNG, DEFDBL, DEFSTR or _DEFINE AS in QB64.


$DYNAMIC arrays can be resized and can retain their remaining element values when used with _PRESERVE in QB64.


Variable values

All numerical variables default to 0 and all string variables default to "" at the start of a program and when first referenced inside of a SUB or FUNCTION procedure except when the variable is defined as a STATIC value.


STATIC sub-procedure values keep their value after the sub-procedure is exited. They will hold an empty value when first used.


Variables are used to hold program data information that is attained through the program flow, either by user input, calculations or by other ways of communicaton (as with I/O, memory, TCP/IP or files).


Assignment of variable values can be done using the = assignment symbol (variable1.number = 500, for example).


Examples

Example of different usages of variables:

max = 1000 DIM d(max) FOR c = 1 TO max d(c) = c + d(c - 1) NEXT PRINT "Show the result of the addition from 1 to n (1+2+3...+n)" PRINT "n = (0-" + LTRIM$(STR$(max)) + "): "; INPUT "", n IF n <= max AND n >= 0 THEN PRINT d(n) ELSE PRINT "Invalid value (only 0 to" + STR$(max) + " is permitted)."

Show the result of the addition from 1 to n (1+2+3...+n) n = (1-1000): 10 55



See also



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