C     AREA OF A TRIANGLE - HERON'S FORMULA
C     INPUT - CARD READER UNIT 5, INTEGER INPUT, NO BLANK CARD FOR END OF DATA
C     OUTPUT - LINE PRINTER UNIT 6, REAL OUTPUT
C     INPUT ERROR DISPAYS ERROR MESSAGE ON OUTPUT
501   FORMAT(3I5)
600   FORMAT("PLEASE ENTER 3 COMMA SEPARATED TRIANGLE SIDE LENGTHS")
601   FORMAT(3HA= ,I5,4H B= ,I5,4H C= ,I5,7H AREA= ,F10.2,10H SQ. UNITS)
602   FORMAT("NORMAL END")
603   FORMAT("INPUT ERROR OR ZERO VALUE ERROR")
      INTEGER A,B,C
      WRITE(6,600)
10    READ(5,501,END=50,ERR=90) A,B,C
      IF(A.EQ.0 .OR. B.EQ.0 .OR. C.EQ.0) GO TO 90
      S = (A + B + C) / 2.0
      AREA = SQRT( S * (S - A) * (S - B) * (S - C))  
      WRITE(6,601) A,B,C,AREA
      GO TO 10
50    WRITE(6,602)
      STOP
90    WRITE(6,603)
      STOP
      END