there r so many ways to define internal table

1. data: begin of itab occurs 100,
         matnr like mara-matnr,
         mtart like mara-mtart,
         end of itab.

2.data: begin of itab.
     include mara.
  data: end of itab.

3. data: begin of itab.
        matnr like mara-matnr,
        mtart like mara-mtart,
        end of itab.
    data: jtab type standard table itab,
          gtab type itab.

4. data: itab like standard table of mara.
   data: jtab like table itab.

5. data: itab like table of mara with header line.