2/19/92 

OUTLINE

Subroutines and Functions

Purposes

Write code once
Reduced size of code
Increased reliability
Improve readability


Write a program which repeatedly prompts the user for two sides of
a right triangle.  Terminate the program when the user has entered zeros
for the sides of the triangles.  Write a subroutine which computes the
hypotenuse of the triangle.  In the main program print out the hypotenuse.

      REAL A,B,H
*
      PRINT *,'Enter 2 sides of a triangle'
      READ *,A,B
*
   10 IF ( A.GT.0.AND.B.GT.0 ) THEN
        CALL HYP(H,A,B)
        PRINT *,'Hypotenuse is ',H
*
        PRINT *,'Enter 2 sides of a triangle'
        READ *,A,B
        GOTO 10 
      ENDIF
      END
      SUBROUTINE HYP(Q,X,Y)
      REAL Q,X,Y
      Q = SQRT(X**2+Y**2)
      RETURN
      END

Execution:

$ a.out
 Enter 2 sides of a triangle
3 4
 Hypotenuse is   5.00000000 
 Enter 2 sides of a triangle
10 20 
 Hypotenuse is   2.236067963E+001 
 Enter 2 sides of a triangle
16 12
 Hypotenuse is   2.561249733E+001 
 Enter 2 sides of a triangle
0,0
$ 

Write the same program as before using a function instead of a subroutine.

      REAL A,B,H
      REAL HYP
*     
      PRINT *,'Enter 2 sides of a triangle'
      READ *,A,B
*
   10 IF ( A.GT.0.AND.B.GT.0 ) THEN
        H = HYP(A,B)
        PRINT *,'Hypotenuse is ',H
*
        PRINT *,'Enter 2 sides of a triangle'
        READ *,A,B
        GOTO 10 
      ENDIF
      END
      FUNCTION HYP(X,Y)
      REAL HYP,X,Y
      HYP = SQRT(X**2+Y**2)
      RETURN
      END

Write the same program using a statement function.


      REAL A,B,H
      REAL HYP
*
      HYP(X,Y) = SQRT(X**2+Y**2)
*     
      PRINT *,'Enter 2 sides of a triangle'
      READ *,A,B
*
   10 IF ( A.GT.0.AND.B.GT.0 ) THEN
        H = HYP(A,B)
        PRINT *,'Hypotenuse is ',H
*
        PRINT *,'Enter 2 sides of a triangle'
        READ *,A,B
        GOTO 10 
      ENDIF
      END

All of these three implementations will produce exactly the same results.