input: Write a function to check whether an array has an even or odd number of elements. Return True if the array has an even number of elements, otherwise return False. If the array is empty, return True as well.
  assert is_array_even([1, 2, 3, 4]) == True
  assert is_array_even([1, 2, 3]) == False
  assert is_array_even([1]) == False
  assert is_array_even([]) == True
output: def is_array_even(arr):
      return len(arr) % 2 == 0