Get element from arbitrary index in set

myset.begin() + 5; only works for random access iterators, which the iterators from std::set are not.

For input iterators, there's the function std::advance:

set<int>::iterator it = myset.begin();
std::advance(it, 5); // now it is advanced by five

In C++11, there's also std::next which is similar but doesn't change its argument:

auto it = std::next(myset.begin(), 5);

std::next requires a forward iterator. But since std::set<int>::iterator is a bidirectional iterator, both advance and next will work.