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