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(0, 0)==None
  assert add(10, -10)==None
  assert add(-1, -1)==None
output: def add(a, b):
      sum = a + b
      print(sum)