module precision_module
implicit none
integer, parameter :: long = selected_real_kind(15,307)
end module precision_module

module maths_module
use precision_module
implicit none
real (long), parameter :: c = 299792458.0_long
! units m s-1
real (long), parameter :: e = 2.71828182845904523_long
real (long), parameter :: g = 9.812420_long
! 9.780 356 m s-2 at sea level on the equator
! 9.812 420 m s-2 at sea level in london
! 9.832 079 m s-2 at sea level at the poles
real (long), parameter :: pi = 3.14159265358979323_long
end module maths_module

module sub1_module
implicit none

contains
  subroutine sub1(radius,area,circum)
  use precision_module
  use maths_module
  implicit none
  real (long), intent (in) :: radius
  real (long), intent (out) :: area, circum

    area = pi*radius*radius
    circum = 2.0_long*pi*radius
  end subroutine sub1
end module sub1_module

program ch2101
use precision_module
use sub1_module
implicit none
real (long) :: r, a, c
integer :: i

  do i = 1, 5
    print *, 'radius?'
    read *, r
    call sub1(r,a,c)
    print *, ' for radius = ', r
    print *, ' area = ', a
    print *, ' circumference = ', c
  end do
end program ch2101