regarding dialg programming

Hello all,

i made a table control with internal table 5 fields.i made Quantity field as an input and output field.

when report run then user change the Quantity field value.

in PAI i made this code

1st in PAI in flow logic i made this .

LOOP at ITAB. ""itab is an internal table

MODULE USER_COMM.

ENDLOOP.

2nd i do this.

MODULE USER_comm INPUT.

CONTROLS: CTR TYPE TABLEVIEW USING SCREEN 102.

modify itab3 INDEX ctr-current_line.

ENDMODULE.

but ctr-current_line value remain 0 due to that a short dump comes messaging that INDEX should not be 0 or less than 0.

can anybody provide me solution.

so that with each iteration of loop ctr-current_line should also increase.

thanks in advance