input: Write a function to add two numbers together and print the result.
  
  def add(a, b):
      sum = a + b
      print(sum)
  
  assert add(5,7)==12
  assert add(3,4)==7
  assert add(0,0)==0
  assert add(-1,1)==0
  assert add(-10,-5)==-15
output: def add(a, b):
      sum = a + b
      print(sum)