A good example showing why to leave comments in your code

comments.cpp

int hash(string input) {
  int output = 5381;
  
  // Less collisions than simply adding ASCII characters of value
  // simple method: hash("tab") = hash("bat")
  // this method: hash("tab") != hash("bat")
  for (char c : input) {
    output += (output << 5) + c;
  }
  
  return output;
}