The '''BYVAL''' statement is used to pass a parameter's value with {{KW|SUB}} programs made in other programming languages.


{{PageSyntax}}
:: Procedure_Name ('''BYVAL''' ''variable1'', '''BYVAL''' ''variable2'')


{{PageDescription}}
* QB64 supports keyword only with [[DECLARE LIBRARY]] [[SUB]] and [[FUNCTION]] procedure declarations. 
* Passing by value assures that the original variable value is not changed by another procedure.
* '''QB64''' can use BYVAL in [[DECLARE LIBRARY]] procedures that add SDL libraries or DLL functions.
* Use [[parenthesis]] around [[SUB]] or [[FUNCTION]] parameters passed BY VALUE in Qbasic or QB64. Ex: ''CALL Procedure ((x&), (y&))''
* Qbasic versions below 7 do not use {{KW|BYVAL}} unless the {{KW|SUB}} program referred to is from a different programming language.
* PDS versions can use {{KW|BYVAL}} as it is intended in any {{KW|SUB}} or {{KW|FUNCTION}} parameters.
*'''BYVAL''' can also be used with [[ABSOLUTE]] in Qbasic but not in QB64 currently.
* '''NOTE: Many Qbasic keyword variable names CAN be used with a [[STRING]] suffix($) ONLY! You CANNOT use them without the suffix, use a numerical suffix or use [[DIM]], [[REDIM]], [[_DEFINE]], [[BYVAL]] or [[TYPE]] variable [[AS]] statements!'''


''Example:'' Passing parameters "by value" using [[parenthesis|brackets]] when calling a [[SUB]] or [[FUNCTION]] in Qbasic or QB64.
{{CodeStart}} '' ''
{{Cl|CALL}} MySUB (a%, (b%), (c%)) 'CALL SUB

MySUB a%, b%, (c%)          'call SUB again without CALL
  
{{Cl|PRINT}} "Outside procedure: "; a%, b%, c%

{{Cl|SUB}} MySUB (a%, b%, c%)
a% = a% + 1: b% = b% + 1: c% = c% + 1
{{Cl|PRINT}} "Inside procedure:  "; a%, b%, c%
{{Cl|END SUB}} '' ''
{{CodeEnd}}
{{OutputStart}}
Inside procedure:  1         1          1
Inside procedure:  2         1          1
Outside procedure: 2         1          0
{{OutputEnd}}
:''Explanation:'' Both SUB calls pass just the '''values''' of b% and c% to the procedure. The first variable, a%, is passed by '''reference''' (the default) so the value was changed by the SUB procedure. Brackets can only be used in the [[CALL]] or function reference!


{{PageSeeAlso}}
* [[DECLARE LIBRARY]]
* [[SUB]], [[FUNCTION]]
* [[DECLARE]], [[DECLARE (non-BASIC statement)]]
* [[CALL]]
* [[Libraries#C++_Variable_Types|C++ Variable Types]]


{{PageNavigation}}