Compilare: user.cpp: In function 'void convex_hull(std::vector<point, std::allocator<point> >&)': user.cpp:61: warning: comparison between signed and unsigned integer expressions user.cpp:101: warning: comparison between signed and unsigned integer expressions user.cpp: In function 'int main()': user.cpp:149: warning: comparison between signed and unsigned integer expressions user.cpp:158: warning: comparison between signed and unsigned integer expressions user.cpp:178: warning: comparison between signed and unsigned integer expressions user.cpp:191: warning: comparison between signed and unsigned integer expressions user.cpp:194: warning: comparison between signed and unsigned integer expressions user.cpp:211: warning: comparison between signed and unsigned integer expressions