Compilare: user.cpp: In function ‘std::vector<point> convex_hull(std::vector<point>&)’: user.cpp:156:37: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < points.size(); ++ i) ^ user.cpp:171:37: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 2; i < points.size(); ++ i) { ^ user.cpp: In function ‘std::vector<point> add_middles(const std::vector<point>&)’: user.cpp:187:41: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < points.size() - 1; ++ i) { ^ user.cpp: In function ‘std::vector<line> get_possible_axes(const std::vector<point>&)’: user.cpp:211:64: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0, j = points.size() / 2; i < points.size() / 2; ++ i, ++ j) ^ user.cpp: In function ‘bool is_axis(const line&)’: user.cpp:218:37: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < points.size(); ++ i) ^