module common
   public :: initial,cross

   contains

   subroutine initial(a,b)
      real, dimension (:), intent(out) :: a,b
      a(1:3) = (/ 2.0, -3.0, -4.0 /)
      b(1:3) = (/ 6.0, 5.0, 1.0 /)
   end subroutine initial

   subroutine cross(r,s)
      real, dimension (:), intent(in) :: r,s
      real, dimension (3) :: cross_product
      ! note use of dummy variables
      integer :: component,i,j
      do component = 1,3
         i = modulo(component,3) + 1
         j = modulo(i,3) + 1
         cross_product(component) = r(i)*s(j) - s(i)*r(j)
      end do
      print *, ""
      print *, "three components of the vector product:"
      print "(a,t10,a,t16,a)", "x","y","z"
      print *, cross_product
   end subroutine cross

   end module common

   program vector            ! illustrate use of arrays
      use common
      real, dimension (3) :: a,b
      real :: dot
      call initial(a,b)
      dot = dot_product(a,b)
      print *, "dot product = ", dot
      call cross(a,b)
   end program vector