Hi Vicky,
Use assign components for the fields instead of sy-index. For example,
ASSIGN COMPONENT: wa_lvc_cat-fieldname OF STRUCTURE <fs_tab_output1>TO <l_field>,
wa_lvc_cat-fieldname OF STRUCTURE <fs_tab_output2> TO <l_field1>.
<l_field1> = <l_field>.
Hope it might help you.
With Regards,
Giriesh M