input: Write a function to check whether an array has an even or odd number of elements. If the array has an even number of elements return True, otherwise return False. If the array is empty then return True.
  assert is_array_even([1, 2, 3, 4])==True
  assert is_array_even([1, 3, 5])==False
  assert is_array_even([])==True
  assert is_array_even([2, 4, 6, 8, 10])==True
  assert is_array_even([7, 9, 11, 13])==False
output: def is_array_even(arr):
      return len(arr) % 2 == 0