Function Module issue

HI Guru s

                  I am practicing FM. I am facing two issue

1) In source code if i use "DATA : ITAB_TABLE....." i get an error ITAB_TABLE is already use.

2) iF i use " DATA : A_TABLE......" i am able to activate it and get 1st o/p screen ,however when i insert the reqd info and click on value i didn't get the reqd info, i have attached all screenshot plz tell me Y  i am not getting output......