C
C  THIS IS AN EXAMPLE OF A PROGRAM MAKING USE OF A SUBPROGRAM.  THE
C  PARTICULAR SUBPROGRAM IN USE IS A FUNCTION WHICH CALCULATES THE AREA 
C  OF A RECTANGLE.  ALL I/O IS THROUGH THE CONSOLE (WITH INPUT USING F10.5 
C  FORMAT).  AN INPUT OF 'Y' OR 'y' WHEN ASKED TO CONTINUE WILL TERMINATE
C  THE PROGRAM.
C
      PROGRAM GEO
      REAL*4 HEIGHT,WIDTH,ANSW,AREA
      CHARACTER*1 MORE
      EXTERNAL AREA
C
C  INPUT THE DATA
C

5     WRITE(6,10)
      READ(5,20)HEIGHT
      WRITE(6,30)
      READ(5,20)WIDTH
C
C  INVOKE THE AREA FUNCTION
C
      ANSW=AREA(HEIGHT,WIDTH)
C
C  OUTPUT THE AREA AND CONTINUE
C
      WRITE(6,40)ANSW
      WRITE(6,50)
      READ(5,60) MORE

      IF(MORE.EQ.'Y'.OR.MORE.EQ.'y') GOTO 5
C
C  FORMAT STATEMENTS
C

10    FORMAT(//'Enter the height of the rectangle ',$)
20    FORMAT(F10.5)
30    FORMAT('Enter the width of the rectangle ',$)
40    FORMAT('The area of the rectangle is ',F10.5)
50    FORMAT('Continue with another input? (Y or N) ',$)
60    FORMAT(A1)

      END

C
C  FUNCTION TO CALCULATE THE AREA OF THE RECTANGLE
C
      REAL FUNCTION AREA(X,Y)
      REAL*4 X,Y

      AREA=X*Y

      RETURN
      END