CALL: Difference between revisions
Jump to navigation
Jump to search
Navigation:
Main Page with Articles and Tutorials
Keyword Reference - Alphabetical
Keyword Reference - By usage
Report a broken link
No edit summary Tags: Undo Reverted |
No edit summary |
||
| (2 intermediate revisions by the same user not shown) | |||
| Line 5: | Line 5: | ||
: [[CALL]] {{Parameter|ProcedureName}} ({{Parameter|parameter1}}, {{Parameter|parameter2}},...)] | : [[CALL]] {{Parameter|ProcedureName}} ({{Parameter|parameter1}}, {{Parameter|parameter2}},...)] | ||
===Alternative syntax=== | === Alternative syntax === | ||
: {{Parameter|ProcedureName}} {{Parameter|parameter1}}, {{Parameter|parameter2}},...] | : {{Parameter|ProcedureName}} {{Parameter|parameter1}}, {{Parameter|parameter2}},...] | ||
{{PageDescription}} | |||
* CALL requires [[SUB]] program parameters to be enclosed in brackets (parenthesis). | * 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. | * CALL is not required to call a subprocedure. Use the SUB-procedure name and list any parameters without parenthesis. | ||
| Line 14: | Line 15: | ||
* To pass parameters by value, instead of by reference, enclose passed variables in parenthesis. | * To pass parameters by value, instead of by reference, enclose passed variables in parenthesis. | ||
=== QBasic/QuickBASIC === | |||
==QBasic/QuickBASIC== | * PDS or QuickBASIC 7 up could use [[BYVAL]] to pass variables by values instead of reference. | ||
* PDS or | |||
* QuickBASIC 4.5 could use [[BYVAL]] only for procedures created in Assembly or another language. | * 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. | * QBasic required [[CALL ABSOLUTE]] only. It did not have to be DECLAREd. | ||
| Line 23: | Line 23: | ||
{{PageExamples}} | {{PageExamples}} | ||
''Example:'' How parameters are passed in two [[SUB]] calls, one with CALL using brackets and one without CALL or brackets: | ''Example:'' How parameters are passed in two [[SUB]] calls, one with CALL using brackets and one without CALL or brackets: | ||
{{CodeStart}} | {{CodeStart}} | ||
{{Cl|DIM}} a {{Cl|AS}} {{Cl|INTEGER}} 'value not shared with SUB | {{Cl|DIM}} a {{Cl|AS}} {{Cl|INTEGER}} 'value not shared with SUB | ||
{{Cl|DIM}} {{Cl|SHARED}} b {{Cl|AS}} {{Cl|INTEGER}} 'value shared with any SUB | {{Cl|DIM}} {{Cl|SHARED}} b {{Cl|AS}} {{Cl|INTEGER}} 'value shared with any SUB | ||
| Line 38: | Line 38: | ||
{{Cl|PRINT}} "Hello World!" | {{Cl|PRINT}} "Hello World!" | ||
{{Cl|PRINT}} a, b, c | {{Cl|PRINT}} a, b, c | ||
a = a + 1 'a is a SUB value of 0 when printed which may increase inside SUB only | 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 | 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 | c = c + 1 'c is a SUB parameter value from a in calls which may increase inside SUB only | ||
{{Cl|END SUB}} | {{Cl|END SUB}} | ||
{{CodeEnd}} | {{CodeEnd}} | ||
| Line 48: | Line 48: | ||
0 2 1 | 0 2 1 | ||
Hello World! | Hello World! | ||
0 3 1 | 0 3 1 | ||
{{OutputEnd}} | {{OutputEnd}} | ||
: ''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. | : ''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. | ||
Latest revision as of 23:10, 2 February 2023
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,...]
Description
- 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