Advice on abap routine in update rule

Question

Hello Experts,
I have written a routine in update for replacing some 'not allowed characters' with space.
The abap code is correctly working as a standalone program as is giving the correct results.However,
when i write the same code in update routine, no change takes place in data, i.e. 'not allowed characters ' are still there in my data.
Please advice if there is any special change that is to be made while writing the code in update routine.
if STRLEN( CHECK_TEXT ) <> 0.
    ALLOWED_SPECIAL_CHARACTERS = ' &()*+,-.:;<>=?!@$%~'.
    ALLOWED_CHARACTERS = 'ABCDEFGHIJKLNMOPQRSTUVWXYZ_0123456789'.
      TRANSLATE CHECK_TEXT TO UPPER CASE.
    strl = strlen( CHECK_TEXT ).
    IF CHECK_TEXT CN ALLOWED_CHARACTERS.
       WHILE len1 LE strl.
        IF CHECK_TEXT+len1(1) CN ALLOWED_CHARACTERS.
        CHECK_TEXT+len1(1) = '.'.
         ENDIF.
       add 1 to len1.
      ENDWHILE.
    ENDIF.
Regards
Priyanka

Answer 1

Thanx a lot for a quick reply .
The main problem that we are facing is this simple code is working fine if it is executed as a report program but if no changes takes place when i move this same code to my update routine.
(1) According to you i should write this routine in the start routine instead of update rotuine ??
(2) how would function module help in my case...kindly elaborate a it.
Here is the complete update rotuine.
data:
len1 TYPE i value 0
R_TEXT(60),
CHECK_TEXT(60),
R_TEXT = COMM_STRUCTURE-/BIC/ZC_NTXT1.
if STRLEN( R_TEXT ) <> 0.
  ALLOWED_SPECIAL_CHARACTERS = ' &()*+,-.:;<>=?!@$%~'.
  CONCATENATE 'ABCDEFGHIJKLNMOPQRSTUVWXYZ_0123456789/'
              ALLOWED_SPECIAL_CHARACTERS
              INTO ALLOWED_CHARACTERS.
  CHECK_TEXT = R_TEXT.
  TRANSLATE CHECK_TEXT TO UPPER CASE.
  strl = strlen( R_TEXT ).
IF CHECK_TEXT CN ALLOWED_CHARACTERS.
      WHILE len1 LE strl.
      subs2 = CHECK_TEXT+len1(1).
        IF subs2 CN ALLOWED_CHARACTERS.
        CHECK_TEXT+len1(1) = '.'.
         ENDIF.
        ENDWHILE.
endif.
    ENDIF.
RESULT = CHECK_TEXT.