program suffices
  integer, parameter :: n = 4
  character(len=2), dimension(0:n) :: &

suffix = (/ 'th', 'st', 'nd', 'rd', 'th' /)
index(m) = min(max(0, modulo(abs(k), 10)), 4)
do k = -100, 100
write(*,'(i4, a)') k, suffix(index(k))
end do
end program suffices