program ch1806
implicit none
integer :: allocate_status = 0
integer, parameter :: n1 = 10000000
integer, parameter :: n2 = 5
integer, dimension (:), pointer :: x
integer, dimension (1:n2), target :: y
integer :: i

  do
    allocate (x(1:n1),stat=allocate_status)
    if (allocate_status>0) then
      print *, ' allocate failed. program ends.'
      stop
    end if
    do i = 1, n1
      x(i) = i
    end do
    do i = 1, n2
      print *, x(i)
    end do
    do i = 1, n2
      y(i) = i*i
    end do
    do i = 1, n2
      print *, y(i)
    end do
! x now points to y
    x => y ! x now points to y
    do i = 1, n2
      print *, x(i)
    end do
! what has happened to the memory that x
! used to point to?
  end do
end program ch1806