How to define a button on Selection-Screen toolbar

Selection-Screen:     Result:     Codes:   report  zanil. * Job: Define button on selection screen. tables: sscrfields. data lv_result type i. data lv_val    type string. * Parameters parameters: p_val1 type i obligatory. parameters: p_val2 type i obligatory. selection-screen function key 1. initialization.   move ‘Sum Values’ to sscrfields–functxt_01. at selection–screen.   if sscrfields–ucomm eq ‘FC01’.      lv_result = p_val1 + p_val2.      lv_val    = lv_result.      message lv_val type ‘S’.      return.   endif.