input: Write a function to determine if the length of an array is even or odd. Return True if the length is even, and False otherwise.
  assert is_array_even([1, 2, 3, 4])==True
  assert is_array_even([1, 2, 3])==False
  assert is_array_even([])==True
output: def is_array_even(arr):
      return len(arr) % 2 == 0