Procedures

Subroutines

Call With Side Effects

A subroutine updates its arguments through intent. call name(args) invokes it.

Program

Play the program to add a bonus into total through a subroutine.

subroutines.f90 
program subroutines_demo
    implicit none
    integer :: total
    total = 10
    call add_bonus(total, 5)
    print '(I0)', total
contains
    subroutine add_bonus(value, bonus)
        integer, intent(inout) :: value
        integer, intent(in) :: bonus
        value = value + bonus
    end subroutine add_bonus
end program subroutines_demo
subroutine `subroutine add_bonus(...)` declares a callable with no return value.
call `call add_bonus(...)` invokes the subroutine.
contains `contains` introduces internal procedures inside a program.