how to program a 'select all' button ?

thanks for all your support..

but the fact is ..i am creating these checkbox at the output list only..it's not a internal table or db field. my program is as follows:

LOOP AT IT_01 INTO WA_01.                                   " IT_01 is the internal table

      WRITE:/1'|', CHK AS CHECKBOX    , 7'|',

            8(18)  WA_01-MATNR COLOR 2,26'|',

           27(10)  WA_01-ERSDA COLOR 3 INTENSIFIED OFF,40'|'.

      HIDE WA_01-MATNR.

  ENDLOOP.

plz help me if u can..thanks