Multi-File Program Structure

Procedure Partition

Keeping Work Behind Calls

A module subroutine can own the calculation while the caller passes data in and receives a result out.

Program

Play the program to choose a quantity and let the module procedure calculate the total.

procedure_partition.f90 
module invoice_mod
    implicit none
contains
    subroutine compute_total(quantity, unit_price, total)
        integer, intent(in) :: quantity
        integer, intent(in) :: unit_price
        integer, intent(out) :: total
        total = quantity * unit_price
    end subroutine compute_total
end module invoice_mod

program procedure_partition_demo
    use invoice_mod, only: compute_total
    implicit none
    integer :: quantity
    integer :: total

    quantity = 
    call compute_total(quantity, 7, total)
    print '(I0, 1X, I0)', quantity, total
end program procedure_partition_demo

module invoice_mod
    implicit none
contains
    subroutine compute_total(quantity, unit_price, total)
        integer, intent(in) :: quantity
        integer, intent(in) :: unit_price
        integer, intent(out) :: total
        total = quantity * unit_price
    end subroutine compute_total
end module invoice_mod

program procedure_partition_demo
    use invoice_mod, only: compute_total
    implicit none
    integer :: quantity
    integer :: total

    quantity = 
    call compute_total(quantity, 7, total)
    print '(I0, 1X, I0)', quantity, total
end program procedure_partition_demo

module invoice_mod
    implicit none
contains
    subroutine compute_total(quantity, unit_price, total)
        integer, intent(in) :: quantity
        integer, intent(in) :: unit_price
        integer, intent(out) :: total
        total = quantity * unit_price
    end subroutine compute_total
end module invoice_mod

program procedure_partition_demo
    use invoice_mod, only: compute_total
    implicit none
    integer :: quantity
    integer :: total

    quantity = 
    call compute_total(quantity, 7, total)
    print '(I0, 1X, I0)', quantity, total
end program procedure_partition_demo
subroutine `compute_total` performs work through arguments instead of returning a value.
intent `intent(in)` and `intent(out)` document data direction across the boundary.
partition The caller stays small because the calculation lives behind a module call.