input: Write a function called add that takes two parameters, a and b, and prints their sum. The function should handle any numerical inputs.
  assert add(5, 7)==12
  assert add(0, 0)==0
  assert add(-1, 1)==0
  assert add(3.5, 2.5)==6.0
  assert add(-3, -2)==-5
output: def add(a, b):
      return a + b