you can write store procedures in C and java also.
just write a procedue in c and crete its dll file.
Then copy this dll file and put it following path
C:\Program Files\IBM\SQLLIB\FUNCTION
C is your drive where you have installed DB2
Now after this create wrapper
Ex.
if your dll file name is abc.dll then
CREATE procedure abc(<Arguments>)
RETURNS <return data type>
NOT FENCED
RETURNS NULL ON NULL INPUT
NO SQL
DBINFO
EXTERNAL ACTION
LANGUAGE C
PARAMETER STYLE DB2SQL
EXTERNAL NAME 'abc!abc';
then it will install procedure in your database and when you call that procedure it will internaly call that procedure which is written in C.