# Function calling
**URL:** https://tech-community.robotics.abb.com/t/function-calling/5261
**Category:** RobotStudio
**Created:** [December 6, 2012, 9:23pm UTC](https://tech-community.robotics.abb.com/t/function-calling/5261 "2012-12-06T21:23:52Z")
**Posts on this page:** 4
**Page:** 1
### Author:  [@phateee](https://tech-community.robotics.abb.com/u/phateee)
#### Post date: [December 6, 2012, 9:23pm UTC](https://tech-community.robotics.abb.com/t/function-calling/5261/1 "2012-12-06T21:23:52Z")
Hello, I am a beginner in programming.I try to make procedure with parametr VAR or INOUT and compiler write me error. I think, that calling procedure with VAR or INOUT is something as pointer in language C/C++. For example:
MODULE A PROC routine(VAR num u)
…
ENDPROC
PROC main()
VAR num x;
routine(x);
ENDPROC
ENDMODULE
And compiler write:
Argument error(124): Argument for ‘VAR’ parameter x is not variable reference or is read only
Thank you for your advice
---
### Author:  [@Henrik\_Berlin](https://tech-community.robotics.abb.com/u/Henrik_Berlin)
#### Post date: [December 6, 2012, 10:45pm UTC](https://tech-community.robotics.abb.com/t/function-calling/5261/2 "2012-12-06T22:45:54Z")
Try this instead:
[CODE]MODULE A
PROC routine(INOUT num u)
u:=2\*u;
ENDPROC
PROC main()
VAR num x:=1;
TPWrite "Before routine: x = "Num:=x;
routine x;
TPWrite "After routine: x = "Num:=x;
ENDPROC
ENDMODULE[/CODE]
You can see the result in the Operator panel below:
---
### Author:  [@Henrik\_Berlin](https://tech-community.robotics.abb.com/u/Henrik_Berlin)
#### Post date: [December 6, 2012, 10:47pm UTC](https://tech-community.robotics.abb.com/t/function-calling/5261/3 "2012-12-06T22:47:26Z")
The RAPID Overview manual contains a description of INOUT, see
[http://www.scribd.com/doc/71173119/Rapid-Overview-Manual#page=112](http://www.scribd.com/doc/71173119/Rapid-Overview-Manual#page=112)
---
### Author:  [@Thomas\_J](https://tech-community.robotics.abb.com/u/Thomas_J)
#### Post date: [December 7, 2012, 5:33pm UTC](https://tech-community.robotics.abb.com/t/function-calling/5261/4 "2012-12-07T17:33:03Z")
The reason you received the above message is because “routine(x)” implies a functin with a return value - the correct use of your format is
x:=routine(x); where routine is defined as a funtion with a return value.
FUNC num routine(num u)
RETURN 2\*u;
ENDFUNC
The instruction call syntax when passing variables or parameters is “routine x;” without ()
functin call syntax is “num:=routine(num);”. with ()
Whenever you use the parentheses () RAPID interprets it as passing parameters to a function that will return a value.
To understand the difference please read the Introduction to RAPID section
| “RAPID instructions and functions” |
| --- |
A RAPID function is similar to an instruction but returns a value
Since the function returns a value, the result of the function can be assigned to a variable. The arguments in a function call are written inside parenthesis and are separated with commas.
An instruction call looks like a procedure call with the instruction name followed by argument values not enclosed in parnthesis.
Hope this helps…