以ZTEST29的flow logic为例，!符号代表区分系统变量名称和自定义的名称。
F1中查看!可以看到示例：
FORM test USING !CHANGING
CHANGING !USING.
using = changing.
ENDFORM.
附:ZTEST29
*&---------------------------------------------------------------------*
*& Report ZTEST29
*&
*&---------------------------------------------------------------------*
*&
*&
*&---------------------------------------------------------------------*
REPORT ztest29.
DATA: gt_sbook TYPE TABLE OF sbook.
DATA: gs_sbook TYPE sbook.
FIELD-SYMBOLS <fs> TYPE STANDARD TABLE.
ASSIGN gt_sbook TO <fs>.
SELECTION-SCREEN BEGIN OF BLOCK blk1.
PARAMETERS p_test LIKE ekko-zywlx.
SELECTION-SCREEN END OF BLOCK blk1.
INITIALIZATION.
MESSAGE 'INITIALIZATION' TYPE 'S'.
AT SELECTION-SCREEN OUTPUT.
MESSAGE 'AT SELECTION-SCREEN OUTPUT' TYPE 'S'.
AT SELECTION-SCREEN.
MESSAGE 'AT SELECTION-SCREEN' TYPE 'S'.
START-OF-SELECTION.
MESSAGE 'START-OF-SELECTION' TYPE 'S'.
PERFORM action.
AT SELECTION-SCREEN ON VALUE-REQUEST FOR p_test.
MESSAGE 'AT SELECTION-SCREEN ON VALUE-REQUEST' TYPE 'S'.
END-OF-SELECTION.
MESSAGE 'END-OF-SELECTION' TYPE 'S'.
FORM action.
SELECT * UP TO 2 ROWS
FROM sbook
INTO TABLE gt_sbook.
gs_sbook-carrid = '001'.
gs_sbook-passname = 'test' && p_test.
APPEND gs_sbook TO <fs>.
LOOP AT <fs> INTO gs_sbook.
WRITE:
/ gs_sbook-carrid,
/ gs_sbook-passname.
ENDLOOP.
ENDFORM.