input: Write a function that adds two numbers together and prints the result.
  
  def add(a, b):
      sum = a + b
      print(sum)
  
  assert add(5, 7) == None
  assert add(-3, 3) == None
  assert add(10, -5) == None
  assert add(0, 0) == None
output: def add(a, b):
      sum = a + b
      print(sum)