CALL sends code execution to a subroutine procedure in a program. In QB64 the subroutine doesn’t need to be declared.
CALL ProcedureName (parameter1, parameter2,…)]
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.
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
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.