input: Write a function to check whether 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.
  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