Customer Exit for Calendar Month based on the day (system Date)

Question

Hello,
I need help in creating a customer exit for Calendar month without the user input. The logic is as follows:
For the BEx variable created with customer exit option and no user input:
If the day on the system date falls in between 1 to 14 take the calendar year/month value as previous month.
If the day on the system date falls in between 15 through 31 then take the calendar year/month as current month.
eg if report is run on March 24th2009 the calendar year/month variable should be calculated as 03/2009 (March 2009)
if the report is run on March 1st2009 the calendar year/month should be calculated as 02/2009 (Feb 2009).
The code should be effective when run in the first 15 days of Jan when the previous month would contain the previous year as well.
Thank You
Srishti

Answer 1

Thanks Shanthi. I am trying to incorporate the logic when the query is run in beginning of Jan when the year should be the previous year.Following is the code.please let me know if it would work. Is there a way I can test it as well?
CASE I_VNAM.
WHEN 'ZCURCALMON'.
IF i_step = 2.
data: mm(2),
        dd(2),
        yy(4),
        FM(6).
if sy-datum+4(2) EQ 1.
sy-datum(4) = sy-datum(4) - 1.
else.
sy-datum(4) = sy-datum(4).
endif.
if sy-datum+6(2) LE 15.
  mm = sy-datum+4(2) - 1.
  concatenate sy-datum(4) mm into FM.
else.
  concatenate sy-datum(4) sy-datum+4(2)  into FM.
endif.
l_s_range-low = FM.
l_s_range-sign = 'I'.
l_s_range-opt = 'EQ'.
append l_s_range to e_t_range.
Endif.
ENDCASE.
Thanks
Srishti