Cm and Inch Conversion - Revisited

Problem Statement

It is known that 1 cm is equal to 0.3937 inch and 1 inch is equal to 2.54 cm. Write a program that uses external functions to convert 0, 0.5, 1, 1.5, ..., 8, 8.5, 9, 9.5, and 10 from cm to inch and from inch to cm. A version using internal functions can be found in an earlier page.

Solution

The following solution has the main program and the two conversion functions in the same file. The order of placing these functions and the main program in the file is unimportant. 
! ---------------------------------------------------------------
!    This program "contains" two REAL functions:
!         (1)  Cm_to_Inch() takes a real inch unit and converts
!              it to cm unit, and
!         (2)  Inch_to_cm() takes a real cm unit and converts it
!              to inch unit.
! The main program uses these functions to convert 0, 0.5, 1, 1.5,
! 2.0, 2.5, ..., 8.0, 8.5, 9.0, 9.5 and 10.0 inch (resp., cm) to
! cm (resp., inch).
! ---------------------------------------------------------------

PROGRAM  Conversion
   IMPLICIT  NONE

   INTERFACE
      REAL FUNCTION  Cm_to_Inch(cm)
         REAL, INTENT(IN) :: cm
      END FUNCTION  Cm_to_Inch

      REAL FUNCTION  Inch_to_Cm(inch)
         REAL, INTENT(IN) :: inch
      END FUNCTION  Inch_to_Cm
   END INTERFACE

   REAL, PARAMETER :: Initial = 0.0, Final = 10.0, Step = 0.5
   REAL            :: x

   x = Initial
   DO                         ! x = 0, 0.5, 1.0, ..., 9.0, 9.5, 10
      IF (x > Final)  EXIT
      WRITE(*,*)  x, 'cm = ',   Cm_to_Inch(x), 'inch and ',  &
                  x, 'inch = ', Inch_to_Cm(x), 'cm'
      x = x + Step
   END DO

END PROGRAM  Conversion

! ---------------------------------------------------------------
! REAL FUNCTION  Cm_to_Inch()
!    This function converts its real input in cm to inch.
! ---------------------------------------------------------------

REAL FUNCTION  Cm_to_Inch(cm)
   IMPLICIT  NONE

   REAL, INTENT(IN) :: cm
   REAL, PARAMETER  :: To_Inch = 0.3937   ! conversion factor

   Cm_to_Inch = To_Inch * cm
END FUNCTION  Cm_to_Inch

! ---------------------------------------------------------------
! REAL FUNCTION  Inch_to_Cm()
!    This function converts its real input in inch to cm.
! ---------------------------------------------------------------

REAL FUNCTION  Inch_to_Cm(inch)
   IMPLICIT  NONE

   REAL, INTENT(IN) :: inch
   REAL, PARAMETER  :: To_Cm = 2.54       ! conversion factor

   Inch_to_Cm = To_Cm * inch
END FUNCTION  Inch_to_Cm
Click here to download this program.

Program Input and Output

The following is the output from the above program. 
 0.E+0cm = 0.E+0inch and 0.E+0inch = 0.E+0cm
 0.5cm = 0.196850002inch and 0.5inch = 1.26999998cm
 1.cm = 0.393700004inch and 1.inch = 2.53999996cm
 1.5cm = 0.590550005inch and 1.5inch = 3.80999994cm
 2.cm = 0.787400007inch and 2.inch = 5.07999992cm
 2.5cm = 0.984250009inch and 2.5inch = 6.3499999cm
 3.cm = 1.18110001inch and 3.inch = 7.61999989cm
 3.5cm = 1.37794995inch and 3.5inch = 8.88999939cm
 4.cm = 1.57480001inch and 4.inch = 10.1599998cm
 4.5cm = 1.77165008inch and 4.5inch = 11.4300003cm
 5.cm = 1.96850002inch and 5.inch = 12.6999998cm
 5.5cm = 2.16534996inch and 5.5inch = 13.9699993cm
 6.cm = 2.36220002inch and 6.inch = 15.2399998cm
 6.5cm = 2.55905008inch and 6.5inch = 16.5100002cm
 7.cm = 2.75589991inch and 7.inch = 17.7799988cm
 7.5cm = 2.95274997inch and 7.5inch = 19.0499992cm
 8.cm = 3.14960003inch and 8.inch = 20.3199997cm
 8.5cm = 3.34645009inch and 8.5inch = 21.5900002cm
 9.cm = 3.54330015inch and 9.inch = 22.8600006cm
 9.5cm = 3.74014997inch and 9.5inch = 24.1299992cm
 10.cm = 3.93700004inch and 10.inch = 25.3999996cm

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