Multi-File Program Structure

Module Constant Use

Shared Settings

A small constants module lets related programs share named settings instead of repeating magic numbers.

Program

Play the program to choose an adjustment and combine it with a module constant.

module_constant_use.f90 
module settings_mod
    implicit none
    integer, parameter :: base_limit = 10
contains
    function adjusted_limit(extra) result(limit)
        integer, intent(in) :: extra
        integer :: limit
        limit = base_limit + extra
    end function adjusted_limit
end module settings_mod

program module_constant_use_demo
    use settings_mod, only: base_limit, adjusted_limit
    implicit none
    integer :: extra
    integer :: limit

    extra = 
    limit = adjusted_limit(extra)
    print '(I0, 1X, I0, 1X, I0)', base_limit, extra, limit
end program module_constant_use_demo

module settings_mod
    implicit none
    integer, parameter :: base_limit = 10
contains
    function adjusted_limit(extra) result(limit)
        integer, intent(in) :: extra
        integer :: limit
        limit = base_limit + extra
    end function adjusted_limit
end module settings_mod

program module_constant_use_demo
    use settings_mod, only: base_limit, adjusted_limit
    implicit none
    integer :: extra
    integer :: limit

    extra = 
    limit = adjusted_limit(extra)
    print '(I0, 1X, I0, 1X, I0)', base_limit, extra, limit
end program module_constant_use_demo

module settings_mod
    implicit none
    integer, parameter :: base_limit = 10
contains
    function adjusted_limit(extra) result(limit)
        integer, intent(in) :: extra
        integer :: limit
        limit = base_limit + extra
    end function adjusted_limit
end module settings_mod

program module_constant_use_demo
    use settings_mod, only: base_limit, adjusted_limit
    implicit none
    integer :: extra
    integer :: limit

    extra = 
    limit = adjusted_limit(extra)
    print '(I0, 1X, I0, 1X, I0)', base_limit, extra, limit
end program module_constant_use_demo
parameter `integer, parameter :: base_limit = 10` names a shared constant.
shared setting The program imports the constant and the helper that uses it.
single source of truth Changing the module constant would update every caller.