Checkbox in a list

If its on a list screen then you can have two button for select all and deselect all and on user command you can use one of the forms below.

form select_all.
  wf_n = 1 .
  do.
    read line wf_n  field value box.
    if sy-subrc ne 0 .
      exit.
    endif.
    if box = space .
      box = 'X'.
      modify line wf_n field value box .
    endif.
    wf_n = wf_n + 1 .
  enddo.
endform.                    " select_all


form deselect_all.
  clear wf_line1.
  clear wf_line.
  wf_n = 1 .
  do.
    read line wf_n  field value box.
    if sy-subrc ne 0 .
      exit.
    endif.
    if box = 'X' .
      box = space.
      modify line wf_n field value box .
      modify line  wf_n  line format color col_normal
      intensified on .
    endif.
    wf_n = wf_n + 1 .
  enddo.
endform.                    " deselect_all

Hope this helps.

Regards

Raja