Compilare: user.cpp: In function 'void convex_hull(std::vector<point, std::allocator<point> >&)': user.cpp:64: warning: comparison between signed and unsigned integer expressions user.cpp:104: warning: comparison between signed and unsigned integer expressions user.cpp: In function 'int main()': user.cpp:153: warning: comparison between signed and unsigned integer expressions user.cpp:162: warning: comparison between signed and unsigned integer expressions user.cpp:182: warning: comparison between signed and unsigned integer expressions user.cpp:195: warning: comparison between signed and unsigned integer expressions user.cpp:198: warning: comparison between signed and unsigned integer expressions user.cpp:215: warning: comparison between signed and unsigned integer expressions