Internal table not getting modified from Table Control

Question

Hi Guys,
I am developing a <b>Module Pool </b>Program where I am inserting data directly in table control of the main screen.
In the flow logic of the Table control I have written :
PROCESS BEFORE OUTPUT.
  LOOP AT itab WITH CONTROL tc1 CURSOR tc1-current_line.
    MODULE read_data.
  ENDLOOP.
MODULE status_0100.
PROCESS AFTER INPUT.
  LOOP AT itab.
    MODULE mod_data.
  ENDLOOP.
MODULE user_command_0100.
Module mod_data input.
MODIFY itab INDEX tc1-current_line.
Endmodule.   
At modify, when I am debugging it's showing sy-subrc = 4 (Entry not appending in Int Table though it is there in the header line). But, if I use append itab, it's working (Problem is that while inserting 2nd record a copy of first record is also appending which I don't want).
Please let me know what's wrong in Modify statement or what is solution for inserting records of tablecontrol in internal table.
TIA,
Nitin

Answer 1

Hi Nitin,
use the following code wor module.
Module mod_data input.
READ ITAB INDEX TC1-CURRENT_LINE.
IF SY-SUBRC = 0.
       MODIFY itab INDEX tc1-current_line.
ELSE.
       APPEND ITAB.
ENDIF.
Endmodule.