input: Write a function to determine if an array has an even or odd number of elements. If the given array has an even number of elements return True else return False. If the given array is empty then return True.
  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