How to calculate the sum of a column in table using ctrl break statements?

Hi,

How to calculate the sum of a column in table using ctrl break statements in smartform:

I want to find the sum of salary in my custom table.

1.I defined footer as Total Text Element.

2.In Code part i write like this :

DATA : ITAB LIKE ZDILEEP OCCURS 0 WITH HEADER LINE.

LOOP AT ITAB INTO ITAB.

AT END OF ZZSALARY.

SUM.

ENDAT.

ENDLOOP.

But its not came....! what i want 2 do...? can anybody help me....?