CALL

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


Syntax

CALL ProcedureName (parameter1, parameter2,...)]

Alternative syntax

ProcedureName parameter1, parameter2,...]


  • CALL requires SUB program parameters to 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 parameters by value, instead of by reference, enclose passed variables in parenthesis.


QBasic/QuickBASIC

  • PDS or Quickbasic 7 up could use BYVAL to pass variables by values instead of reference.
  • QuickBASIC 4.5 could use BYVAL only for procedures created in Assembly or another language.
  • QBasic required CALL ABSOLUTE only. It did not have to be DECLAREd.


Examples

Example: How parameters are passed in two SUB calls, one with CALL using brackets and one without CALL or brackets:

DIM a AS INTEGER 'value not shared with SUB DIM SHARED b AS INTEGER 'value shared with any SUB a = 1 b = 2 c = 3 CALL helloworld (a) 'a passed to c parameter with CALL helloworld a 'a passed to c parameter w/o CALL END SUB helloworld (c) 'SUB parameter variables are always inside of brackets in SUB code PRINT "Hello World!" PRINT a, b, c a = a + 1 'a is a SUB value of 0 when printed which may increase inside SUB only b = b + 1 'b is a shared value which can increase anywhere c = c + 1 'c is a SUB parameter value from a in calls which may increase inside SUB only END SUB

Returns:

Hello World! 0 2 1 Hello World! 0 3 1

Explanation: Variable a that is outside of the subroutine isn't SHARED so it will have no effect inside the subroutine, the variable a inside the subroutine is only valid inside the subroutine, and whatever value a has outside of it makes no difference within the subroutine.
The variable b on the other hand is SHARED with the subroutines and thus can be changed in the subroutine. The variable a is initiated with 0 as default when created, thus it will return 0 since it wasn't changed within the subroutine.
The variable 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 c variable value outside of the sub is irrelevant within the subroutine.


See also



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