Customer Exit code written at transaction SE38

Question

I am new to writing ABAP code. I talk to someone on here earlier and they gave me some code that is indented below to determine the last day of the week as a date. I am trying to use this code in a form that is called from a user exit. However, I do not understand what the code is doing. I added some break points and found out the the variables CurDate TYPE SCAL-DATE, and
CurWeek TYPE SCAL-WEEK never populate with a date or a value. So my first question is why don't these variables populate with a value? My second question is how do I write the final desired value (LastDayOfTheWeek) back to the customer exit variable? My third question is to explain TYPE-POOLS: RSR, RRS0 and how they relate to i_t_var_range, e_t_range, and l_s_range. Are these standard variables used in customer exits or are these custom to the environment that I am working at? I know this is alot to ask, but I have no other place to get information. Thanks for all the help possible.
-- Ryan
*& Subroutine pool   ZBW_VAR_WEEKEND
*& Created By: Ryan Casey
*& Date: 07/19/2005
*& Purpose: This function is used to determine the date of the last
*&          day of the week (Sunday).
*& Changes:
PROGRAM  ZBW_VAR_WEEKEND.
TYPE-POOLS:  RSR,
             RRS0.
Form GetWeekendDate  using     i_t_var_range type rrs0_t_var_range
                               i_step type i
                     changing  e_t_range type rsr_t_rangesid.
                          DATA: l_s_range TYPE rsr_s_rangesid,
                                CurDate TYPE SCAL-DATE,
                                CurWeek TYPE SCAL-WEEK,
                                LastDayOfTheWeek TYPE SCAL-DATE.
                          CALL FUNCTION 'DATE_GET_WEEK'
                          EXPORTING
                          DATE = CurDate
                          IMPORTING
                          WEEK = CurWeek
                          EXCEPTIONS
                          DATE_INVALID.
                          CALL FUNCTION 'WEEK_GET_FIRST_DAY'
                          EXPORTING
                          WEEK = CurWeek
                          IMPORTING
                          DATE = LastDayOfTheWeek
                          EXCEPTIONS
                          WEEK_INVALID.
                          ADD 6 TO LastDayOfTheWeek.
*&l_s_range-low    = LastDayOfTheWeek.
*&l_s_range-sign   = 'I'.
*&l_s_range-opt    = 'EQ'.
*&APPEND l_s_range to e_t_range.
Endform.

Answer 1

Hi Ryan,
I thought it was related to BW since the message is posted in the BW forum and accordingly suggested a formula in the update rule, so you would not find it as a FM in R/3. The following code should do it.
data : p_week type KWEEK,
       p_Date type SYDATUM.
p_week = <incoming value in week of year>
CALL FUNCTION 'WEEK_GET_FIRST_DAY'
  EXPORTING
    week               = p_week
IMPORTING
   DATE               = p_date
EXCEPTIONS
   WEEK_INVALID       = 1
   OTHERS             = 2
IF sy-subrc <> 0.
MESSAGE ID SY-MSGID TYPE SY-MSGTY NUMBER SY-MSGNO
         WITH SY-MSGV1 SY-MSGV2 SY-MSGV3 SY-MSGV4.
ENDIF.
To get the last day of the week.
p_date = p_date + 6.
You can find the available fm in the system from se37 transaction code.
Cheers, Ashu