input: Write a function to determine whether an array has an even or odd number of elements. If the number of elements in the array is even, return True, otherwise return False. If the array is empty, it should be treated as having an even number of elements.
  assert is_array_even([1, 2, 3, 4])==True
  assert is_array_even([1, 2, 3])==False
  assert is_array_even([])==True
  assert is_array_even([5, 6, 7, 8, 9])==False
output: def is_array_even(arr):
      return len(arr) % 2 == 0