initially I felt like all of them should be cost in the public for fear of changing data, I wont lie, I did some checking around on here on the forums and deduced that it will not be all of them. Given I looked around, I believe all but bool fBullCowGame::CheckGuessValidity(std::string), now my logic may be poor, though I believe since it contains std::string it stands out to me as one that may require some more flexibility than that others. Could be completely wrong.
Edit: Forgot about reset -.-, video covered it xD