Compilare: user.cpp: In function ‘void lower_hull(int, std::vector<std::pair<int, int> >, std::vector<std::pair<int, int> >)’: user.cpp:45:30: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < B.size(); i++) p.push_back(B[i]); ^ user.cpp:53:30: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 1; i < p.size(); i++) ^ user.cpp:54:25: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (i == p.size() - 1 || cross_product(p1,p[i],p2) > 0) ^