input: Write a function to print out an array backwards.
  assert print_reverse_array([1, 2, 3, 4, 5])==None
  assert print_reverse_array([10, 20, 30, 40, 50])==None
  assert print_reverse_array([])==None
output: def print_reverse_array(arr):
      for i in range(len(arr)-1, -1, -1):
          print(arr[i])