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66 lines
3 KiB
Plaintext
66 lines
3 KiB
Plaintext
[[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|parameter1}}, {{Parameter|parameter2}},...)]
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===Alternative syntax===
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: {{Parameter|ProcedureName}} {{Parameter|parameter1}}, {{Parameter|parameter2}},...]
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* CALL requires [[SUB]] program parameters to 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 parameters by value, instead of by reference, enclose passed variables in parenthesis.
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==QBasic/QuickBASIC==
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* PDS or Quickbasic 7 up could use [[BYVAL]] to pass variables by values instead of reference.
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* QuickBASIC 4.5 could use [[BYVAL]] only for procedures created in Assembly or another language.
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* QBasic required [[CALL ABSOLUTE]] only. It did not have to be DECLAREd.
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{{PageExamples}}
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''Example:'' How parameters are passed in two [[SUB]] calls, one with CALL using brackets and one without CALL or brackets:
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{{CodeStart}} '' ''
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{{Cl|DIM}} a {{Cl|AS}} {{Cl|INTEGER}} 'value not shared with SUB
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{{Cl|DIM}} {{Cl|SHARED}} b {{Cl|AS}} {{Cl|INTEGER}} 'value shared with any SUB
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a = 1
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b = 2
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c = 3
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{{Cl|CALL}} helloworld (a) 'a passed to c parameter with CALL
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helloworld a 'a passed to c parameter w/o CALL
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{{Cl|END}}
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{{Cl|SUB}} helloworld (c) 'SUB parameter variables are always inside of brackets in SUB code
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{{Cl|PRINT}} "Hello World!"
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{{Cl|PRINT}} a, b, c
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a = a + 1 'a is a SUB value of 0 when printed which may increase inside SUB only
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b = b + 1 'b is a shared value which can increase anywhere
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c = c + 1 'c is a SUB parameter value from a in calls which may increase inside SUB only
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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 2 1
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Hello World!
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0 3 1
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{{OutputEnd}}
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: ''Explanation:'' Variable '''{{Parameter|a}}''' that is outside of the subroutine isn't [[SHARED]] so it will have no effect inside 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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:The variable '''{{Parameter|c}}''' is the [[SUB]] parameter variable that passes values into the sub. Its value could be changed by the passed parameter value or inside of the subroutine. The un-shared '''{{Parameter|c}}''' variable value outside of the sub is irrelevant within the subroutine.
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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}}
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