How to avoid declaring and setting the value of a variable in each subroutine?

Question

How to avoid repeated declaration of a variable that has a constant value in subroutines?

For example:

program test
  implicit none

  integer :: n
  integer :: time

  print*, "enter n" ! this will be a constant value for the whole program
  call Calcul(time)
  print*, time  
end program

subroutine Calcul(Time)
  implicit none

  integer :: time 

  ! i don't want to declare the constant n again and again because some times the subroutines have a lot of variables.  
  time = n*2 
end subroutine

Sometimes there are a lot of constants that are defined by the user and I will make a lot of subroutines that use those constants, so I want to stock them and and use them without redefining them again and again.

You have to use modules. Also, do not call n a constant. It is a variable. You are changing it in the read statement. — Vladimir F Героям слава
– Vladimir F Героям слава, Commented Feb 27, 2017 at 10:52
See stackoverflow.com/questions/42024559/… and stackoverflow.com/questions/19040118/… stackoverflow.com/questions/1240510/… and others (possible duplicate. — Vladimir F Героям слава
– Vladimir F Героям слава, Commented Feb 27, 2017 at 10:55

Vladimir F Героям слава · Accepted Answer · 2017-02-27 14:27:52Z

5

For global variables use modules (old FORTRAN used common blocks, but they are obsolete):

module globals
  implicit none

  integer :: n

contains

  subroutine read_globals()    !you must call this subroutine at program start

    print*, "enter n" ! this will be a constant value for the whole program
    read *, n
  end subroutine
end module

!this subroutine should be better in a module too !!!
subroutine Calcul(Time)
  use globals !n comes from here
  implicit none

  integer :: time 
  time = n*2
end subroutine

program test
  use globals ! n comes from here if needed
  implicit none

  integer :: time

  call read_globals()

  call Calcul(time)

  print*, time
end program

There are many questions and answers explaining how to use Fortran modules properly on Stack Overflow.

answered Feb 27, 2017 at 14:27

Vladimir F Героям слава

60.7k4 gold badges82 silver badges131 bronze badges

Sign up to request clarification or add additional context in comments.

4 Comments

Mohammed Aqlan Over a year ago

Thanks that works very well and easy, is there another way without using modules?

Vladimir F Героям слава Over a year ago

Yes, with common blocks. I don't recommend them at all. Modern Fortran is all about modules so you should learn to use them as much as possible.

Vladimir F Героям слава Over a year ago

In simple cases you can also make the subroutine to be internal to the program (put it between contains and end program.

Mohammed Aqlan Over a year ago

The best solution I think is using module, thank you for your help!!

Collectives™ on Stack Overflow

How to avoid declaring and setting the value of a variable in each subroutine?

1 Answer 1

4 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

4 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related