Selection-screen fields validation for dialog

Question

Hello ABAP Gurus
Requirements: this is a report wherein , depending upon the correct select-options , user will pick some field values from table and some will be entered by the user in the next se51 custom screen for creation of a record in a ztable .
the problem is :without validating select-options values , it calls the se51 screen 100.
How to keep the cursor at the selection-screen field until & unless user enters the correct i/p s .if i/p are correct then only it should call screen 100 otherwise remain in the selection screen only .
*& Report ZSD_REP_QUOT_BANK_CREATE *
REPORT ZSD_REP_QUOT_BANK_CREATE NO STANDARD PAGE HEADING LINE-SIZE 255.
TABLES: VBAK,VBAP,VBRK,ZSD_TABL_QOTBANK,MARA,KONV.
DATA: OK_CODE LIKE SY-UCOMM,
SAVE_OK_CODE LIKE SY-UCOMM,
WA_ITAB LIKE ZSD_TABL_QOTBANK,
ANSWER TYPE C,
COPIED ,
STS TYPE N,
EMGRP LIKE MARA-EXTWG,
QTY LIKE ZSD_TABL_QOTBANK-QTY,
UPRICE LIKE ZSD_TABL_QOTBANK-UPRICE,
TOT LIKE ZSD_TABL_QOTBANK-TOT,
INO LIKE VBAP-POSNR.
SELECTION-SCREEN BEGIN OF BLOCK b1 WITH FRAME TITLE text-000.
SELECT-OPTIONS: S_QTNO FOR ZSD_TABL_QOTBANK-QTNO
NO INTERVALS NO-EXTENSION OBLIGATORY,
S_ITNO FOR ZSD_TABL_QOTBANK-ITNO
NO INTERVALS NO-EXTENSION OBLIGATORY.
S_MATNO FOR ZSD_TABL_QOTBANK-MATNO
NO INTERVALS NO-EXTENSION. "
SELECTION-SCREEN END OF BLOCK b1.
AT SELECTION-SCREEN.
SELECT SINGLE VBTYP
INTO VBAK-VBTYP
FROM VBAK
WHERE VBELN IN S_QTNO.
IF SY-SUBRC EQ 0 AND VBAK-VBTYP NE 'B'.
MESSAGE I005(ZQOTBANK).
SET CURSOR FIELD S_QTNO-LOW.
SUBMIT (SY-REPID) VIA SELECTION-SCREEN.
ENDIF.
CLEAR WA_ITAB.
SELECT SINGLE QTNO ITNO
INTO WA_ITAB
FROM ZSD_TABL_QOTBANK
WHERE QTNO IN S_QTNO
AND ITNO IN S_ITNO.
IF SY-SUBRC EQ 0.
MESSAGE I001(ZQOTBANK).
SET CURSOR FIELD S_QTNO-LOW.
SET CURSOR FIELD S_ITNO-LOW.
SUBMIT (SY-REPID) VIA SELECTION-SCREEN.
ENDIF.
*START-OF-SELECTION.
END-OF-SELECTION.
CALL SCREEN 0100.
*& Module STATUS_0100 OUTPUT
text
MODULE STATUS_0100 OUTPUT.
SET PF-STATUS '0100'.
SET TITLEBAR '0100'.
ZSD_TABL_QOTBANK-QTNO = S_QTNO-LOW.
SELECT SINGLE BUKRS_VF VKORG VTWEG SPART KUNNR ERDAT BNDDT
KNUMV
INTO (ZSD_TABL_QOTBANK-CCODE,
ZSD_TABL_QOTBANK-SORG,
ZSD_TABL_QOTBANK-DISTCHAN,
ZSD_TABL_QOTBANK-DIV,
ZSD_TABL_QOTBANK-CUSTNO,
ZSD_TABL_QOTBANK-QTDAT,
ZSD_TABL_QOTBANK-QTVALDAT,
VBAK-KNUMV)
FROM VBAK
WHERE VBELN IN S_QTNO
AND VBTYP = 'B'.
IF SY-SUBRC EQ 0.
SELECT SINGLE KWMENG POSNR MATNR
INTO (QTY , INO , ZSD_TABL_QOTBANK-MATNO)
FROM VBAP
WHERE VBELN IN S_QTNO.
SELECT SINGLE EXTWG
INTO EMGRP
FROM MARA
WHERE MATNR EQ ZSD_TABL_QOTBANK-MATNO.
ZSD_TABL_QOTBANK-ITNO = INO.
ZSD_TABL_QOTBANK-EMATGRP = EMGRP.
ZSD_TABL_QOTBANK-QTY = QTY.
SELECT SINGLE KBETR
INTO UPRICE
FROM KONV
WHERE KNUMV = VBAK-KNUMV
AND KPOSN = INO
AND KSCHL = 'PR00'.
ENDIF.
ZSD_TABL_QOTBANK-UPRICE = UPRICE.
TOT = QTY * UPRICE .
ZSD_TABL_QOTBANK-TOT = TOT .
CLEAR: QTY, UPRICE, TOT.
QTY = ZSD_TABL_QOTBANK-CGL_QTY.
UPRICE = ZSD_TABL_QOTBANK-CGL_UPRICE .
TOT = QTY * UPRICE .
ZSD_TABL_QOTBANK-CGL_TOT = TOT .
CLEAR: QTY, UPRICE, TOT.
QTY = ZSD_TABL_QOTBANK-BHEL_QTY.
UPRICE = ZSD_TABL_QOTBANK-BHEL_UPRICE .
TOT = QTY * UPRICE .
ZSD_TABL_QOTBANK-BHEL_TOT = TOT .
CLEAR: QTY, UPRICE, TOT.
QTY = ZSD_TABL_QOTBANK-BHEL_QTY.
UPRICE = ZSD_TABL_QOTBANK-BHEL_UPRICE .
TOT = QTY * UPRICE .
ZSD_TABL_QOTBANK-BHEL_TOT = TOT .
CLEAR: QTY, UPRICE, TOT.
QTY = ZSD_TABL_QOTBANK-ALSTOM_QTY.
UPRICE = ZSD_TABL_QOTBANK-ALSTOM_UPRICE .
TOT = QTY * UPRICE .
ZSD_TABL_QOTBANK-ALSTOM_TOT = TOT .
CLEAR: QTY, UPRICE, TOT.
QTY = ZSD_TABL_QOTBANK-SIEMENS_QTY.
UPRICE = ZSD_TABL_QOTBANK-SIEMENS_UPRICE .
TOT = QTY * UPRICE .
ZSD_TABL_QOTBANK-SIEMENS_TOT = TOT .
CLEAR: QTY, UPRICE, TOT.
QTY = ZSD_TABL_QOTBANK-TELK_QTY.
UPRICE = ZSD_TABL_QOTBANK-TELK_UPRICE .
TOT = QTY * UPRICE .
ZSD_TABL_QOTBANK-TELK_TOT = TOT .
CLEAR: QTY, UPRICE, TOT.
QTY = ZSD_TABL_QOTBANK-OTH_QTY.
UPRICE = ZSD_TABL_QOTBANK-OTH_UPRICE .
TOT = QTY * UPRICE .
ZSD_TABL_QOTBANK-OTH_TOT = TOT .
CLEAR: QTY, UPRICE, TOT.
ENDMODULE. " STATUS_0100 OUTPUT
*& Module USER_COMMAND_0100 INPUT
text
MODULE USER_COMMAND_0100 INPUT.
CASE OK_CODE.
WHEN 'SAVE'.
INSERT ZSD_TABL_QOTBANK.
IF SY-SUBRC EQ 0.
MESSAGE I000(ZQOTBANK).
COMMIT WORK.
CALL SELECTION-SCREEN 1000.
ELSE.
MESSAGE E001(ZQOTBANK).
CALL SELECTION-SCREEN 1000.
ENDIF.
ENDCASE.
ENDMODULE. " USER_COMMAND_0100 INPUT
*& Module EXIT_COMMAND INPUT
text
MODULE EXIT_COMAND INPUT.
SAVE_OK_CODE = OK_CODE.
CLEAR OK_CODE.
CASE SAVE_OK_CODE.
WHEN 'CANCEL'.
CALL FUNCTION 'POPUP_TO_CONFIRM'
EXPORTING
TITLEBAR = 'Quotation Bank Entry'
TEXT_QUESTION = 'Do you want to Cancel ?'
TEXT_BUTTON_1 = 'Yes'
TEXT_BUTTON_2 = 'No'
DEFAULT_BUTTON = '2'
IMPORTING
ANSWER = ANSWER.
IF ANSWER = '1'.
LEAVE PROGRAM.
ELSE.
CALL SELECTION-SCREEN 1000.
ENDIF.
WHEN 'EXIT'.
CALL FUNCTION 'POPUP_TO_CONFIRM'
EXPORTING
TITLEBAR = 'Quotation Bank Entry'
TEXT_QUESTION = 'Do you want to Exit ?'
TEXT_BUTTON_1 = 'Yes'
TEXT_BUTTON_2 = 'No'
DEFAULT_BUTTON = '2'
IMPORTING
ANSWER = ANSWER.
IF ANSWER = '1'.
LEAVE PROGRAM.
ELSE.
CALL SELECTION-SCREEN 1000.
ENDIF.
ENDCASE.
ENDMODULE. " EXIT_COMMAND INPUT
Thnx in Advance

Answer 1

Put the statement
CALL SCREEN 100
in the event <b>AT SELECTION-SCREEN</b> and NOT in <b>END-OF-SELECTION</b>.
Regards,
Subramanian V.