Why "Modify itab index sy-tabix." makes internal table content blank?

Question

We have an internal table itab which looks like to have the following content:
A---B---C
1----3----
2----2----
We would like to get the column C value in this internal table itab by summing Column A and Column B, and then fill C column values into this internal table. We know that the program would looks like:
Loop at itab into wa_itab.
    wa_itab-C = wa_itab-A + wa_itab-B.
    Modify itab index sy-tabix.
EndLoop.
But after executing the above code, all itab becomes blank. Through debugging, find it's caused by the statement "Modify itab index sy-tabix.".  Could any ABAP expert here let us know the reason and we will give you reward points!

Answer 1

hi,
what you tried is correct.but instead of using
modify itab index sy-tabix
use
modify itab index sy-tabix from wa_itab.
the reason for blank data is you are not mentioning from where that record is to be updated.your specifying the record using index.one thing is no need to use index also because in a loop you are modifying so automatically it will take you to the record.
try the following code.
types:begin of it,
     a type i,
     b type i,
     c type i,
     end of it.
data:itab type standard table of it.
data:wa_itab type it.
wa_itab-a = 3. wa_itab-b = 4.
append wa_itab to itab.
Loop at itab into wa_itab.
    wa_itab-C = wa_itab-A + wa_itab-B.
Modify itab index sy-tabix from wa_itab.
*you can use Modify itab from wa_itab.
EndLoop.
loop at itab into wa_itab.
write:wa_itab-a,wa_itab-b,wa_itab-c.
endloop.
<REMOVED BY MODERATOR>
Edited by: Alvaro Tejada Galindo on Apr 8, 2008 5:49 PM