Using AT FIRST , AT NEW, AT THE END OF , AT LAST

DATA: BEGIN OF ITAB OCCURS 0,
F1 TYPE I,
F2(6) TYPE C,
F3(10) TYPE N,
F4(16) TYPE P DECIMALS 2,
END OF ITAB.
DATA: SUB_TOT(10) TYPE P DECIMALS 3.
**--1
ITAB-F1 = 1.
ITAB-F2 = 'ONE'.
ITAB-F3 = 10.
ITAB-F4 = '1000.00'.
APPEND ITAB.
CLEAR ITAB.
ITAB-F1 = 1.
ITAB-F2 = 'ONE'.
ITAB-F3 = 20.
ITAB-F4 = '2000.00'.
APPEND ITAB.
CLEAR ITAB.
ITAB-F1 = 1.
ITAB-F2 = 'ONE'.
ITAB-F3 = 30.
ITAB-F4 = '3000.00'.
APPEND ITAB.
CLEAR ITAB.
*--2
ITAB-F1 = 2.
ITAB-F2 = 'TWO'.
ITAB-F3 = 10.
ITAB-F4 = '1000.00'.
APPEND ITAB.
CLEAR ITAB.
ITAB-F1 = 2.
ITAB-F2 = 'TWO'.
ITAB-F3 = 20.
ITAB-F4 = '2000.00'.
APPEND ITAB.
CLEAR ITAB.
*-- 3
ITAB-F1 = 3.
ITAB-F2 = 'THREE'.
ITAB-F3 = 10.
ITAB-F4 = '1000.00'.
APPEND ITAB.
CLEAR ITAB.
ITAB-F1 = 3.
ITAB-F2 = 'THREE'.
ITAB-F3 = 20.
ITAB-F4 = '2000.00'.
APPEND ITAB.
CLEAR ITAB.
SORT ITAB BY F1.
LOOP AT ITAB.
AT FIRST.
WRITE: /35 ' MATERIAL DETAILS:'.
ULINE.
ENDAT.
AT NEW F1.
WRITE: / 'DETAILS OF MATERIAL:' COLOR 7 , ITAB-F1.
ULINE.
ENDAT.
WRITE: / ITAB-F1, ITAB-F2, ITAB-F3, ITAB-F4.
SUB_TOT = SUB_TOT + ITAB-F4.
AT END OF F1.
ULINE.
WRITE: / 'SUB TOTAL :' COLOR 3 INVERSE ON, SUB_TOT COLOR 3 INVERSE ON.
CLEAR SUB_TOT.
ENDAT.
AT LAST.
SUM.
ULINE.
WRITE: 'SUM:', ITAB-F4.
ULINE.
ENDAT.
ENDLOOP.