How to set selection screen

Question

I have a question that ...
i have 2 options --
when select 1st option , show group1 screen
when select 2nd option, show group2 screen
like the follow ..which is pretty work!....but i have another question that how to set the screen field ..
my question is that if i select group1 screen...i want to set
if S1_EBELN = '' and S1_IHREZ = ''.
    message e398 with 'pls input one of these two options!'.
  elseif S1_EBELN ne '' and S1_IHREZ ne ''.
    message e398 with 'Only one of these two options input is allowed！'.
  endif.
i've tried to insert these statement within the LOOP...but not work ......
so can anyone know how to set?
PARAMETERS:
R1 RADIOBUTTON GROUP OPT1 USER-COMMAND R DEFAULT 'X'.
PARAMETERS:
R2 RADIOBUTTON GROUP OPT1.
SELECTION-SCREEN BEGIN OF BLOCK RPT1 WITH FRAME TITLE TEXT-001.
SELECTION-SCREEN SKIP 1.
SELECT-OPTIONS: S1_BUKRS FOR EKKO-BUKRS MODIF ID ABC. 
SELECT-OPTIONS: S1_EBELN FOR EKKO-EBELN MODIF ID ABC . 
SELECT-OPTIONS: S1_IHREZ FOR EKKO-IHREZ MODIF ID ABC .  
SELECTION-SCREEN END OF BLOCK RPT1.
SELECTION-SCREEN BEGIN OF BLOCK RPT2 WITH FRAME TITLE TEXT-001.
SELECTION-SCREEN SKIP 1.
SELECT-OPTIONS:  S2_BUKRS FOR EKKO-BUKRS MODIF ID DEF.
SELECT-OPTIONS: S2_MBLNR FOR MKPF-MBLNR MODIF ID DEF.   
SELECT-OPTIONS: S2_XBLNR FOR MKPF-XBLNR MODIF ID DEF .   
SELECTION-SCREEN END OF BLOCK RPT2.
IF R1 = 'X'.
    LOOP AT SCREEN.
      IF screen-group1 = 'DEF'.
        screen-input = '1'.
        SCREEN-required = '1'.
        SCREEN-INVISIBLE = '1'.
        screen-input = '0'.
        screen-output = '1'.
        screen-active = '0'.
        MODIFY SCREEN.
      ENDIF.
    ENDLOOP.
ELSEIF R2 = 'X'.
    LOOP AT SCREEN.
      IF screen-group1 = 'ABC' .
        screen-active = '0'.
        screen-input = '0'.
        screen-output = '1'.
        MODIFY SCREEN.
      ENDIF.
    ENDLOOP.
  ENDIF.

Answer 1

Modified ur code .
tables : ekko, mkpf.
PARAMETERS : R1 RADIOBUTTON GROUP RG USER-COMMAND R DEFAULT 'X'.
PARAMETERS : R2 RADIOBUTTON GROUP RG .
SELECTION-SCREEN BEGIN OF BLOCK RPT1 WITH FRAME TITLE TEXT-001.
SELECTION-SCREEN SKIP 1.
SELECT-OPTIONS: S1_BUKRS FOR EKKO-BUKRS MODIF ID ABC.
SELECT-OPTIONS: S1_EBELN FOR EKKO-EBELN MODIF ID ABC .
SELECT-OPTIONS: S1_IHREZ FOR EKKO-IHREZ MODIF ID ABC .
SELECTION-SCREEN END OF BLOCK RPT1.
SELECTION-SCREEN BEGIN OF BLOCK RPT2 WITH FRAME TITLE TEXT-001.
SELECTION-SCREEN SKIP 1.
SELECT-OPTIONS: S2_BUKRS FOR EKKO-BUKRS MODIF ID DEF.
SELECT-OPTIONS: S2_MBLNR FOR MKPF-MBLNR MODIF ID DEF.
SELECT-OPTIONS: S2_XBLNR FOR MKPF-XBLNR MODIF ID DEF .
SELECTION-SCREEN END OF BLOCK RPT2.
at selection-screen output.
IF R1 = 'X'.
LOOP AT SCREEN.
IF screen-group1 = 'DEF' .
screen-active = '0'.
MODIFY SCREEN.
ENDIF.
ENDLOOP.
ENDIF.
IF R2 = 'X'.
LOOP AT SCREEN.
IF screen-group1 = 'ABC' .
screen-active = '0'.
MODIFY SCREEN.
ENDIF.
ENDLOOP.
ENDIF.
at selection-screen .
if r1 = 'X'.
if s1_ebeln[] is initial and s1_ihrez[] is initial..
message e001(zxx) with 'pls input one of these two options!'.
endif.
if NOT s1_ebeln[] IS initial.
IF NOT s1_ihrez[] IS INITIAL.
message e001(zxx) with 'only one entry in Ebeln or Ihrez is
allowed'.
ENDIF.
ENDIF.
endif.
START-OF-SELECTION.
WRITE:/ 'hi'.
***add on
split the text into two texts .
<b>if NOT s1_ebeln[] IS initial.
IF NOT s1_ihrez[] IS INITIAL.
message e001(zxx) with text-001 text-002.
*'only one entry in Ebeln   = text-001
or Ihrez is allowed'.       = text-002.</b> 
regards,
vijay