input: Write a function to add two numbers together and print the result. Define the function header as `def add(a,b):`. Include assert statements to verify the correctness of the function. Ensure the function outputs the correct results for the given assert statements.
  
  def add(a, b):
      sum = a + b
      print(sum)
  
  assert add(5, 7)==12
  assert add(10, -3)==7
  assert add(0, 0)==0
  assert add(-1, -1)==-2
output: def add(a, b):
      sum = a + b
      print(sum)