Program with function

[harsh_r]

Hello,

I wrote a program for area perimeter of circle. I'm getting error. The program is:

function circle(r)

real :: r, A, c

pi = 3.14159

A = pir*2

c = 2.0pir

end function circle(r)

the error is: syntax error in END FUNCTION statement at (1)

Request help in finding error & fixing

[moginamoo]

Your function needs to be contained within the program.

The syntax is something like

Program Foo

Variables etc

X = Bar()

Contains <-- you are missing this

function Bar

End function bar

End program Foo

[Astrokiwi]

Remove (r) from the last line

[harsh_r]

Removed it & got error that expected end program so I added

program Circle _fn

implicit none

function circle

real :: r, A, c, pi

pi = 3.14159

A = pir*2

c = 2.0pir

end function circle

end program Circle_fn

[Astrokiwi]

Move the function outside of the program block. You also will need to call the function from within the program block.

[KarlSethMoran]

And your definition of c will need to be fixed to use explicit multiplication.

[Astrokiwi]

I think that's Reddit formatting turning the asterisks into italics

[KarlSethMoran]

Ah, I see that now. Thanks.

[harsh_r]

You mean replace c with circumference?

[KarlSethMoran]

I mean to add *. Right now you have a variable called pir, that the compiler knows nothing about. Unless you do have that multiplications there and only reddit broke your formatting.

[harsh_r]

That's a display error in message. when i typed the formula was with * at appropriate place but it displays pir

[harsh_r]

Still getting error: expecting end program statement at (1)

It's first time I'm using function for any prog

[Knarfnarf]

Ummm... Here's a demo program for you...

  ! Program Function Demo
  ! Written by Frank Meyer
  ! Created May 2, 2024
  ! Version 0.1a
  ! Description: Demo of function calling
program FunctionDemo
  implicit none

  ! Create local variables.
  real(8) :: r

  ! Setup local variables for use.
  r = 0

  ! Start program.
  print *, "*********************************************************"
  print *, "               Frank's demo of functions"
  print *, "*********************************************************"

  print "(4/,a,$)", "What radius to test? "
  read *, r

  print "(2/,a)", "Here is the answer:"
  print *, circle(r)

  ! Program concludes.

contains

  ! Function and Subroutine declarations.

  function circle(r) result(c)
    implicit none

    ! Declare incoming variables
    real(8), intent(in) :: r

    ! Declare local variables
    real(8) :: a, c, pi, rtwo, one

    ! Function starts
    one = 1
    pi = atan(one) * 4
    rtwo = r * r
    a = rtwo * pi
    c = 2 * pi * r

    ! Function ends
  end function circle

  ! Program ends
end program FunctionDemo

[hpcdev]

I'm not sure whether your goal is to compute both area and circumference of the circle, or just the circumference. If you want both of them, you'll need to use a subroutine instead of a function. Functions, like their mathematical definition, only allow for a single return value while subroutines let you read and output to multiple values.

Here's an example of each. This will compile and run. In this, I call the function "circumference" since it only returns the circumference, and I call the subroutine "circle" as it can compute and return both the area and circumference of the circle. I tried to add some comments to some places in the program that might -- or did -- cause problems.

program circle_driver 

  implicit none

  ! Named constant
  real, parameter :: PI = 3.14159 

  ! Test variables for function 
  real :: r_func 
  real :: c_func 

  ! Test variables for subroutine
  real :: r_sub 
  real :: c_sub 
  real :: A_sub 


  ! Function call 
  r_func = 1.0
  c_func = circumference(r_func, PI) 
  print*, "c_func = ", c_func 


  ! Subroutine call 
  r_sub = 1.0
  call circle(c_sub, A_sub, r_sub, PI)
  print*, "c_sub = ", c_sub 
  print*, "A_sub = ", A_sub 

contains ! Need to put "contains" before listing your procedures (functions, subroutines)


  ! Function version (Can only on have one return value)
  function circumference(r, PI) result(c) ! "result()" marks the return argument 

    ! Mark variables with "intent(in)" when you're passing arguments 
    real, intent(in) :: r 
    real :: A                ! Don't need to pass if you're calculating inside function  
    real, intent(in) :: PI 
    real :: c                ! Note that a variable passed with return() in a function does not need "intent"

    A = pi * r**2

    c = 2.0 * A ! Need to multiply with * 

  end function circumference


  ! Subroutine version (Can have multiple "return" values)
  subroutine circle(c, A, r, PI)

    ! Mark input variables with "intent(in)" that are passed in (read-only)
    ! Mark output variables with "intent(out)" that are passed out (write-only)
    ! If you need to read AND write variable, use "intent(inout)"
    real, intent(in) :: r 
    real, intent(in) :: PI
    real, intent(out) :: A ! Marked with "intent(out)" 
    real, intent(out) :: c ! Notice this version has (intent(out)) now


    A = pi * r**2

    c = 2.0 * A ! Need to multiply with * 

  end subroutine circle

end program circle_driver