input: Write a python function to determine if a number is even or odd.
  assert is_even_or_odd(4) == "The number is Even."
  assert is_even_or_odd(7) == "The number is Odd."
  assert is_even_or_odd(0) == "The number is Even."
output: def is_even_or_odd(n):
      if n % 2 == 0:
          return "The number is Even."
      else:
          return "The number is Odd."