input: Write a function to determine if an array has an even or odd number of elements. The function should return True if the number of elements is even, otherwise return False. If the array is empty, it should return True.
  
  assert is_array_even([1, 2, 3, 4])==True
  assert is_array_even([1, 2, 3, 4, 5])==False
  assert is_array_even([])==True
output: def is_array_even(arr):
      return len(arr) % 2 == 0