Creating own functions - programmers guide

[chrizio]

Hi,

I didn't manage to find on the OOo portal any good guide
about creating / programming own Calc functions.
I have to write some functions to be used in my Calc sheet.
Where can I study the underlying programming language ?

My current question on writing user defined functions is following:
The function shall take some number of cells containing one integer
pro cell as an array - input parameter.
How must be such function be defined ?

[chrizio]

Calc is someway strange.

Why does following function

FUNCTION aaa(ByVal x As INTEGER) As INTEGER
DIM s%
s=x
return s
End Function

generate compiling error as below ?
"Basic syntax error - label s undefined" <- message translated from German

The function is placed in My Macros->Standard->xxxx

[Villeroy]

The StarBasic language is fairly documented in the online-help. You may use other languages like java, python, C++, C#, Jscript.
Developer's guide:
http://api.openoffice.org/docs/DevelopersGuide/DevelopersGuide.xhtml
API reference:
http://api.openoffice.org/docs/common/ref/com/sun/star/module-ix.html
The appropriate forums on this site:
http://www.oooforum.org/forum/viewforum.phtml?f=9
http://www.oooforum.org/forum/viewforum.phtml?f=11
Short answer:
A sheet-cell function passes and returns strings, doubles or errors.
The basic language has an undocumented keyword "return", but I do not know what it's good for. The return-value of a Basic-function has to be assigned to the function's name:

[noranthon]

I use "return" in conjunction with GoSub.

Other values are mentioned in the API index R but none seem relevant here.
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[JohnV]

You return the value of a function by setting the function name = value so try
aaa = s
instead of
return s.

[chrizio]

Thanks for all answers.

That with return xxxx I have found just in forum or in help.
It wasn't my own invention.