qb64/internal/help/CALL.txt

{{KW|CALL}} sends code execution to a subroutine procedure in a program. In '''QB64''' the subroutine doesn't need to be declared.


{{PageSyntax}}
::: '''CALL {{Parameter|ProcedureName}}''' ['''('''{{Parameter|parameters}}, {{Parameter|passed}},...''')''']


''Non-call Syntax:'' 

::: '''{{Parameter|ProcedureName}}''' [{{Parameter|parameters}}, {{Parameter|passed}},...]


* CALL requires that {{KW|SUB}} program parameters be enclosed in brackets(parenthesis).
* CALL is NOT required to call a subprocedure. Use the SUB-procedure name and list any parameters without parenthesis.
* Neither syntax can be used to call [[GOSUB]] linelabel sub procedures.
* To pass by values, both syntaxes require that each of those variable names be enclosed in parenthesis.
* PDS or Quickbasic 7 up can use [[BYVAL]] to pass by values instead of reference.
* Quickbasic 4.5 can use [[BYVAL]] only for procedures created in Assembly or another language.
* Qbasic requires [[CALL ABSOLUTE]] only. It does not have to be [[DECLARE]]d.


''Example:''
{{CodeStart}} '' ''
{{Cl|DIM}} a {{Cl|AS}} {{Cl|INTEGER}}
{{Cl|DIM}} {{Cl|SHARED}} b {{Cl|AS}} {{Cl|INTEGER}}
a = 1
b = 1
{{Cl|CALL}} helloworld
{{Cl|CALL}} helloworld

{{Cl|SUB}} helloworld
{{Cl|PRINT}} "Hello World!"
{{Cl|PRINT}} a
{{Cl|PRINT}} b
a = a + 1
b = b + 1
{{Cl|END SUB}} '' ''
{{CodeEnd}}

''Returns:''
{{OutputStart}}Hello World!
 0
 1
Hello World!
 0
 2 {{OutputEnd}}
: ''Explanation:'' When the subroutine is [[CALL]]ed the code inside the subroutine is executed until it reaches the [[END SUB]] statement or an [[EXIT SUB]] statement. Since the variable {{Parameter|a}} that is outside of the subroutine isn't [[SHARED]] it will have no effect in the subroutine, the variable {{Parameter|a}} inside the subroutine is only valid inside the subroutine, and whatever value {{Parameter|a}} has outside of it makes no difference within the subroutine.

:The variable {{Parameter|b}} on the other hand is [[SHARED]] with the subroutines and thus can be changed in the subroutine. The variable {{Parameter|a}} is initiated with 0 as default when created, thus it will return 0 since it wasn't changed within the subroutine.

:''Note:'' CALL doesn't need to be used in order to call a subroutine. Adding the name of the sub to the code like this will do:

::::::'''{{text|helloworld|green}}'''

: Also; note that the variable {{Parameter|a}} outside of the subroutine is different from the variable {{Parameter|a}} inside the subroutine since {{Parameter|a}} isn't {{KW|SHARED}} through subroutines, variable {{Parameter|b}} on the other hand is {{KW|SHARED}} through subroutines and thus is the same within the subroutine as outside of it.


{{PageSeeAlso}}
* [[SUB]], [[FUNCTION]]
* [[DECLARE]], [[DECLARE (non-BASIC statement)]]


{{PageNavigation}}