programming Quadratic equation using functions on fortran 95

Question

I am trying to create a program that uses the quadratic formula. However, I want to do it entirely with external functions on fortran 95. My program keeps giving me weird errors regarding "inconsistent types" and etc.

This is what I have so far. If anyone has suggestions on where I could be wrong, I would greatly appreciate it.

Thanks a lot!

   PROGRAM Quad
IMPLICIT NONE

    !Function & variable Declaration
    CHARACTER(1):: response='X'
    INTEGER:: a=0, b=0, c=0, iost=0, disc=0
    INTEGER:: EnterA, EnterB, EnterC, FindDiscriminate
    REAL:: FindUniqueSolution, FindRealSolution1, FindRealSolution2
    REAL:: x=0, x1=0, x2=0

    !Open statement
    OPEN(UNIT=23,FILE = "solutions.txt", ACTION = "WRITE", STATUS="NEW",IOSTAT=iost)
    IF (iost>0) STOP "Problem opening the file!"


    a=EnterA ()
    b=EnterB ()
    c=EnterC ()
    disc=FindDiscriminate (a,b,c)




DO
    PRINT*, "Find the solution(s) for equation of type: Ax^2 + Bx + C = 0"
    PRINT*, "A, B, and C should each be integers in the range -999 to 999!"

    PRINT*, "YOUR EQUATION: ",a,"x^2 +",b,"x +",c,"=0"
    PRINT*, "DISCRIMINATE: ",disc
    WRITE(23,'(1X,A,I3,A,I3,A,I3,A)',IOSTAT=iost),"YOUR EQUATION: ",a,"x^2 +",b,"x +",c,"=0"
    IF (iost>0) STOP "Problem opening the file!"

    IF (disc==0) THEN
        x=FindUniqueSolution (a,b,c,disc)
        PRINT*, "ONE REAL SOLUTION: ",x
        WRITE(23,'(1X,A,T35,F4.1)',IOSTAT=iost),"ONE REAL SOLUTION: ",x
        IF (iost>0) STOP "Problem writing to the file!"
    ELSE IF(disc>0) THEN
        PRINT*, "TWO REAL SOLUTIONS: "
        x1=FindRealSolution1 (a,b,c,disc)
        PRINT*, "REAL SOLUTION 1: ",x1
        x2=FindRealSolution2 (a,b,c,disc)
        PRINT*, "REAL SOLUTION 2: ",x2
        WRITE(23,'(1X,A)',IOSTAT=iost),"TWO REAL SOLUTIONS"
        WRITE(23,'(1X,A,T35,F4.1)',IOSTAT=iost),"REAL SOLUTION 1: ",x1
        WRITE(23,'(1X,A,T35,F4.1)',IOSTAT=iost),"REAL SOLUTION 2: ",x2
        IF (iost>0) STOP "Problem writing to the file!"
    ELSE
        PRINT*, "Your equation is unsolvable (the discriminant is less than 0)."
    END IF

    WRITE (*,'(1X,A)',ADVANCE="NO"),"Do another(y/n)?"
    READ*, response
    IF (response /= "y") EXIT

END DO

    CLOSE(23)



END PROGRAM

!Begin External Functions ----------------------------------------------------------

INTEGER FUNCTION EnterA ()
IMPLICIT NONE
INTEGER:: a=0

DO
    WRITE (*,'(1X,A)',ADVANCE="NO"),"Enter A: "
    READ*, a
    IF (a <= -999 .AND. a >= 999) EXIT
    PRINT*, "Must be an integer between -999 and 999. TRY AGAIN!"
END DO

EnterA=a

END FUNCTION EnterA

! New External Function ------------------------------------------------------------------------------

INTEGER FUNCTION EnterB ()
IMPLICIT NONE
INTEGER:: b=0

DO
    WRITE (*,'(1X,A)',ADVANCE="NO"),"Enter B: "
    READ*, b
    IF (b <= -999 .AND. b >= 999) EXIT
    PRINT*, "Must be an integer between -999 and 999. TRY AGAIN!"
END DO

EnterB=b

END FUNCTION EnterB
!-----------------------------------------------------------------------------------
INTEGER FUNCTION EnterC ()
IMPLICIT NONE
INTEGER:: c=0

DO
    WRITE (*,'(1X,A)',ADVANCE="NO"),"Enter C: "
    READ*, c
    IF (c <= -999 .AND. c >= 999) EXIT
    PRINT*, "Must be an integer between -999 and 999. TRY AGAIN!"
END DO

EnterC=c

END FUNCTION EnterC
!---------------------------------------------------------------------------------

INTEGER FUNCTION FindDiscriminate(a,b,c)
IMPLICIT NONE
INTEGER:: disc=0

INTEGER, INTENT(IN):: a,b,c

disc=INT(b**2)-(4*a*c)

FindDiscriminate=disc
END FUNCTION FindDiscriminate
!----------------------------------------------------------------------------------

REAL FUNCTION FindUniqueSolution (a,b,c,disc)
IMPLICIT NONE
REAL:: x

REAL, INTENT(IN):: a,b,c,disc

x=REAL(-b)/(2.0*a)

FindUniqueSolution=x
END FUNCTION FindUniqueSolution
!---------------------------------------------------------------------------------

REAL FUNCTION FindRealSolution1 (a,b,c,disc)
IMPLICIT NONE
REAL:: x1

REAL, INTENT (IN):: a,b,c,disc

x1=REAL(-b+disc)/(2.0*a)

FindRealSolution1=x1
END FUNCTION FindRealSolution1
!---------------------------------------------------------------------------------

REAL FUNCTION FindRealSolution2 (a,b,c,disc)
IMPLICIT NONE
REAL:: x2

REAL, INTENT (IN):: a,b,c,disc

x2=REAL(-b-disc)/(2.0*a)

FindRealSolution2=x2
END FUNCTION FindRealSolution2

I've no idea about your inconsistent types but I did notice that you forgot to take the square root of your discriminant. — Neil, Mar 29 '11 at 19:18
"If anyone has suggestions on where I could be wrong, I would greatly appreciate it." - Well, for a start; stop using so many functions. (unless there is a very good reason for it! Is there?) — Rook, Mar 29 '11 at 19:34
It is odd that you are declaring so many variables as integers for a quadratic equation. Probably somewhere the compiler is highlighting a difference in type between actual and dummy argument. It would help if you gave specific error messages, including showing which lines were called out by the compiler. — M. S. B., Mar 29 '11 at 20:24
There's a few odd things here. Nonetheless, the code as posted compiles correctly for me with gfortran and ifort (although it runs incorrectly; the if test in enterA/b/c is backwards, there doesn't really need to be a separate function for each variable, etc). Is there a reason why you want the functions to be external, but in the same file -- as opposed to in a CONTAINS statement in the program, or in a module? — Jonathan Dursi, Mar 29 '11 at 20:42
there is also a capital error in your logic: `a <= -999 .AND. a >= 999` if a is in the range -999:999, then it will be false, if a is smaller than -999, false, and if a is larger than 999, also false. So it will always evaluate to false... (edit: the previous comment seems to already mention this) — steabert, Mar 30 '11 at 09:26

score 2 · Answer 1 · answered Mar 29 '11 at 21:48

2

In your main program you reference the functions FindUniqueSolution, FindRealSolution1, and FindRealSolution2. You pass a,b,c, and disc as arguments. These are declared as integers, but inside those functions the corresponding dummy arguments are declared as reals. So, there's your type mismatch.

answered Mar 29 '11 at 21:48

eriktous

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2

As somewhat already suggested, you would probably get a clearer error message if you put the functions into a module and "used" the module in the program. That would make the interfaces "explicit". And you wouldn't need to declare the functions in your main program. – M. S. B. Mar 29 '11 at 23:38
@M. S. B.: I fully agree with putting all functions in a module (or making them internal), but even as is gfortran gave me a crystal clear error message, identifying this problem. – eriktous Mar 30 '11 at 10:12

programming Quadratic equation using functions on fortran 95

1 Answers1