input: Write a function to determine if an array has an even or odd number of elements. If the number of elements is even, 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([])==True
  assert is_array_even([5, 6, 7, 8, 9])==False
output: def is_array_even(arr):
      return len(arr) % 2 == 0