STL distance is what you need. Std::distance(set.begin(), find_result).
Std::set has just a bidirectional iterator, which means you can't do what you're trying to do with operator + (or -). Those are only available to random access iterators, like std::vector provides.
I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.