Help with Customer exit variable

Question

Hi Guys,
     I need your urgent help. I have a requirement where I need to create a variable (on CALDAY) in a report which should use the input value given for another variable (created on CALMONTH). To put in words more clearly, CALMONTH is a variable that is mandatory for input but the CALDAY variable should not appear on the selection screen. I was told that I should write a customer exit to make this happen. So can someone please explain me the process of creating a customer exit and give me the code.
WHEN CALMONTH values are selected to be 07/2006 - 08/2006... CALDAY values should be 07/01/2006 to 08/31/2006.
CALMONTH is user entry, mandatory, range and multiple selection variable.
  Early reply is highly appreciated and duely rewarded. Please let me know if I am not clear about the requirement. Thanks a bunch in advance.

Answer 1

Let us say, user enters multiple ranges for the month, you would want corresponding date ranges for the same, right?
data : w_date like sy-datum.
case I_VNAM.
when 'ZCALDAY'. " Calday var
loop at i_t_var_range into LOC_VAR_RANGE         
     where iobjnm = 'ZCALMONTH'.
  WA_RANGE-SIGN = 'I'.     
  wa_date+2(6) = loc_var_Range-low.
  wa_date+0(2) = '01'.
  wa_range-low = wa_date.
  if loc_var_range-high eq space.
    WA_RANGE-OPT = 'EQ'.     
  else.
    wa_range-opt = 'BT'.
    wa_date+2(6) = loc_var_range-high.
    wa_date+0(2) = '01'.
    wa_date = wa_date + 31.
    wa_date+0(2) = '01'.
    wa_date = wa_date - 1.
    wa_range-high = wa_date.
   endif.
   append wa_range to e_t_range. clear wa_range.
endloop.
endcase.
This should do.