Customer exit first day of the month from the user entered date

Hi Friends,

I have a requirement where i need to calculate first day of the month from the user entered date. I did this procedure but did not get the desired output.

1) Created a user entry variable on delivery date. Say " ZDEL_DTE"

2) Created a Customer exit on delivery date " ZEXIT_DEL_DATE" and gave intervel to it and disabled user entry.

3) Wrote this code in CMOD:

Data: l_s_range TYPE rrrangesid,
       loc_var_range LIKE rrrangeexit,

        lv_month TYPE d,
       lv_year(4) TYPE n,

       lv_data type sy-datum,

       lv_data1 type sy-datum.

CASE I_VNAM.

When 'ZEXIT_DEL_DATE'

IF I_STEP = 2.

LOOP AT i_t_var_range into loc_var_range WHERE vnam = 'ZDEL_DTE'.

lv_month = loc_var_range-low+4(2).
       lv_year = loc_var_range-low+0(4).

CONCATENATE lv_year lv_month '01' INTO lv_DATA.

           lv_data1  = loc_var_range-low.
           l_s_range-low  = lv_first_day.
           l_s_range-sign = 'I'.
           l_s_range-opt  = 'BT'.

           APPEND l_s_range TO e_t_range.
         ENDLOOP.

When i am executing say 29th jan 2015, it should get the data from 1st to 29th of jan. But it is getting only 29th of jan. Where have i gone wrong. Please give  alight on this.

I used this post as a ref and did that. link : Customer Exit for 1st day of the month til the date user entered