fortran 77 sample

C AREA OF A TRIANGLE - HERON'S FORMULA
C INPUT - CARD READER UNIT 5, INTEGER INPUT
C OUTPUT - LINE PRINTER UNIT 6, REAL OUTPUT
C INPUT ERROR DISPAYS ERROR MESSAGE ON OUTPUT
      PROGRAM AREA
      INTEGER A, B, C
      CHARACTER MSGEND*40, MSGERR*40
      MSGEND = "NORMAL END"
      STRERR = "INPUT ERROR"

  100 READ(5,10,END=200,ERR=300) A,B,C
   10 FORMAT(3I5)
      IF(A=0 .OR. B=0 .OR. C=0) THEN
         WRITE(6,*) "Zero value not allowed"
      ELSE
         S = (A + B + C) / 2.0
         AREA = SQRT( S * (S - A) * (S - B) * (S - C))
         WRITE(6,601) A,B,C,AREA
   20    FORMAT(" A=",I5,", B=",I5,", C=",I5,", AREA=",
     *      F10.2," SQUARE UNITS")
      END IF
      GO TO 100

  200 WRITE(6,*) MSGEND
      STOP
  300 WRITE(6,*) MSGERR
      STOP
      END