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