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.
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.
来源：https://stackoverflow.com/questions/42483715/how-to-avoid-declaring-and-setting-the-value-of-a-variable-in-each-subroutine