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63 lines
No EOL
2.7 KiB
Text
63 lines
No EOL
2.7 KiB
Text
{{KW|CALL}} sends code execution to a subroutine procedure in a program. In '''QB64''' the subroutine doesn't need to be declared.
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{{PageSyntax}}
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::: '''CALL {{Parameter|ProcedureName}}''' ['''('''{{Parameter|parameters}}, {{Parameter|passed}},...''')''']
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''Non-call Syntax:''
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::: '''{{Parameter|ProcedureName}}''' [{{Parameter|parameters}}, {{Parameter|passed}},...]
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* CALL requires that {{KW|SUB}} program parameters be enclosed in brackets(parenthesis).
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* CALL is NOT required to call a subprocedure. Use the SUB-procedure name and list any parameters without parenthesis.
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* Neither syntax can be used to call [[GOSUB]] linelabel sub procedures.
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* To pass by values, both syntaxes require that each of those variable names be enclosed in parenthesis.
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* PDS or Quickbasic 7 up can use [[BYVAL]] to pass by values instead of reference.
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* Quickbasic 4.5 can use [[BYVAL]] only for procedures created in Assembly or another language.
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* Qbasic requires [[CALL ABSOLUTE]] only. It does not have to be [[DECLARE]]d.
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''Example:''
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{{CodeStart}} '' ''
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{{Cl|DIM}} a {{Cl|AS}} {{Cl|INTEGER}}
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{{Cl|DIM}} {{Cl|SHARED}} b {{Cl|AS}} {{Cl|INTEGER}}
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a = 1
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b = 1
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{{Cl|CALL}} helloworld
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{{Cl|CALL}} helloworld
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{{Cl|SUB}} helloworld
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{{Cl|PRINT}} "Hello World!"
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{{Cl|PRINT}} a
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{{Cl|PRINT}} b
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a = a + 1
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b = b + 1
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{{Cl|END SUB}} '' ''
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{{CodeEnd}}
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''Returns:''
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{{OutputStart}}Hello World!
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0
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1
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Hello World!
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0
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2 {{OutputEnd}}
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: ''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.
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: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.
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:''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:
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::::::'''{{text|helloworld|green}}'''
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: 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.
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{{PageSeeAlso}}
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* [[SUB]], [[FUNCTION]]
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* [[DECLARE]], [[DECLARE (non-BASIC statement)]]
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{{PageNavigation}} |