CALL - mkilgore/QB64pe GitHub Wiki

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.

• 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.

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

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.

• SUB, FUNCTION
• DECLARE, DECLARE (non-BASIC statement)