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.
  assert is_array_even([1, 2, 3, 4])==True
  assert is_array_even([1, 2, 3])==False
  assert is_array_even([1, 2, 3, 4, 5, 6, 7, 8])==True
  assert is_array_even([1])==False
  assert is_array_even([])==True
output: def is_array_even(arr):
      return len(arr) % 2 == 0