Compilare: user.cpp: In function 'void convex_hull1(std::vector<point, std::allocator<point> >&)': user.cpp:82: warning: comparison between signed and unsigned integer expressions user.cpp:122: warning: comparison between signed and unsigned integer expressions user.cpp: In function 'int main()': user.cpp:159: warning: comparison between signed and unsigned integer expressions user.cpp:168: warning: comparison between signed and unsigned integer expressions user.cpp:188: warning: comparison between signed and unsigned integer expressions user.cpp:201: warning: comparison between signed and unsigned integer expressions user.cpp:204: warning: comparison between signed and unsigned integer expressions user.cpp:221: warning: comparison between signed and unsigned integer expressions