Indexfile creation

      IDENTIFICATION DIVISION.
       PROGRAM-ID.  index.
       ENVIRONMENT DIVISION.
       INPUT-OUTPUT SECTION.
       FILE-CONTROL.
           SELECT STDFILE ASSIGN TO DISK
           ORGANIZATION IS INDEXED
           ACCESS MODE IS SEQUENTIAL
           RECORD KEY SNO.
       DATA DIVISION.
       FILE SECTION.
       FD STDFILE
      LABEL RECORDS ARE STANDARD
    VALUE OF FILE-ID IS "STD.DAT".      
  01 STDREC.
      02 SNO PIC 9(5).
      02 SNM PIC X(10).
      02 M PIC 9(3).
       WORKING-STORAGE SECTION.
       77 CH PIC X VALUE SPACE.
       PROCEDURE DIVISION.
       MAIN-PARA.
           OPEN OUTPUT STDFILE.
           PERFORM READ-DATA UNTIL CH = "N" OR "n".
           CLOSE STDFILE.
           STOP RUN.
       READ-DATA.
      /     MOVE SPACE TO CH.
           DISPLAY "ENTER STUDENT NUMBER: ".
           ACCEPT SNO.
           DISPLAY "ENTER STUDENT NAME: ".
           ACCEPT SNM.
           DISPLAY "ENTER MARKS SCORED: ".
           ACCEPT M.
           WRITE STDREC INVALID KEY
  DISPLAY " INVALID DATA ".
           DISPLAY "CONTINUE (Y/N)".
           ACCEPT CH.