Help with user exit

Hi Experts,

I have the fallowing prob

I have

Cube : ZIC_C03

Query : ZSTKREP

I need to create a variable(ZLTRDAY) on info object 0postng_date of the above cube based on the values i enter in the varialble 0REDAY1. I need to get the last posting date in that month.

for ex : i give dates like 01.01.2009 to 27.01.2009 in the variable "0reday1" but if the last transaction in that month is done on 22.01.2009 then the variable should get the value 22.01.2009 for that variable as i need to create a RKF based on variable ZLTRDAY

I have no Idea of ABAP coding. Can you guys help me with the code.