ABAP : loop at screen

DATA: sen(40).

PARAMETERS : p_cat TYPE c RADIOBUTTON GROUP g01 USER-COMMAND uc1 DEFAULT 'X'.
SELECTION-SCREEN BEGIN OF LINE .
SELECTION-SCREEN POSITION 5.
PARAMETERS : p_lovely AS CHECKBOX MODIF ID r01 .
SELECTION-SCREEN COMMENT 7(10) TEXT-c01.
SELECTION-SCREEN END OF LINE.

SELECTION-SCREEN BEGIN OF LINE.
SELECTION-SCREEN POSITION 5.
PARAMETERS : p_smart AS CHECKBOX MODIF ID r01.
SELECTION-SCREEN COMMENT 7(10) TEXT-c02.
SELECTION-SCREEN END OF LINE.
SELECTION-SCREEN ULINE.


PARAMETERS : p_dog TYPE c RADIOBUTTON GROUP g01.
SELECTION-SCREEN BEGIN OF LINE.
SELECTION-SCREEN POSITION 5.
PARAMETERS : p_angry  AS CHECKBOX MODIF ID r02.
SELECTION-SCREEN COMMENT 7(10) TEXT-d01.
SELECTION-SCREEN END OF LINE.

SELECTION-SCREEN: BEGIN OF LINE,
                  POSITION 5.
PARAMETERS : p_nice AS CHECKBOX MODIF ID r02.
SELECTION-SCREEN: COMMENT 7(10) TEXT-d02,
                  END OF LINE.

AT SELECTION-SCREEN OUTPUT.
  LOOP AT SCREEN.
    IF p_cat = 'X' AND screen-group1 = 'R02'.
      p_nice = ''.
      p_angry = ''.
      screen-input = '0'.
      MODIFY SCREEN.
    ELSEIF p_dog = 'X' AND screen-group1 = 'R01'.
      p_lovely = ''.
      p_smart =''.
      screen-input = '0'.
      MODIFY SCREEN.
    ENDIF.

  ENDLOOP.

START-OF-SELECTION.

  IF p_cat ='X'.
    CONCATENATE sen 'You love cat that' INTO sen.
    IF p_lovely ='X'.
      CONCATENATE sen TEXT-c01 INTO  sen SEPARATED BY space.
    ENDIF.

    IF p_smart = 'X'.
      CONCATENATE sen 'and' TEXT-c02 INTO sen SEPARATED BY space.
    ENDIF.

  ELSE.
    CONCATENATE sen 'You love dog that' INTO sen .
    IF p_angry = 'X'.
      CONCATENATE sen TEXT-d01 INTO  sen SEPARATED BY space.
    ENDIF.

    IF p_nice = 'X'.
      CONCATENATE sen 'and' TEXT-d02 INTO sen SEPARATED BY space.
    ENDIF.
  ENDIF.

  sen = abap_false.

  WRITE sen.