mirror of
https://github.com/QB64Official/qb64.git
synced 2024-07-16 21:15:15 +00:00
63 lines
2.3 KiB
Markdown
63 lines
2.3 KiB
Markdown
|
[CALL](CALL) sends code execution to a subroutine procedure in a program. In **QB64** the subroutine doesn't need to be declared.
|
||
|
|
|
||
|
|
## Syntax
|
||
|
|
|
||
|
|
> [CALL](CALL) ProcedureName (parameter1, parameter2,...)]
|
||
|
|
|
||
|
|
### Alternative Syntax
|
||
|
|
|
||
|
|
> ProcedureName parameter1, parameter2,...]
|
||
|
|
|
||
|
|
* CALL requires [SUB](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](GOSUB) linelabel sub procedures.
|
||
|
|
* To pass parameters by value, instead of by reference, enclose passed variables in parenthesis.
|
||
|
|
|
||
|
|
## Example(s)
|
||
|
|
|
||
|
|
How parameters are passed in two [SUB](SUB) calls, one with CALL using brackets and one without CALL or brackets:
|
||
|
|
|
||
|
|
```vb
|
||
|
|
|
||
|
|
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:*
|
||
|
|
|
||
|
|
```text
|
||
|
|
|
||
|
|
Hello World!
|
||
|
|
0 2 1
|
||
|
|
Hello World!
|
||
|
|
0 3 1
|
||
|
|
|
||
|
|
```
|
||
|
|
|
||
|
|
> *Explanation:* Variable **a** that is outside of the subroutine isn't [SHARED](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](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](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
|
||
|
|
|
||
|
|
* [SUB](SUB), [FUNCTION](FUNCTION)
|