Compilare: user.cpp: In function ‘void convex_hull(std::vector<std::pair<int, int> >)’: user.cpp:26:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 1; i < a.size(); ++i) ^ user.cpp:33:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 3; i < a.size(); ++i){ ^ user.cpp: In function ‘int main()’: user.cpp:93:39: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0; i < a.size() - 1; ++i, X = 1 - X){ ^ user.cpp:97:46: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int NR = 0; NR < Points.size(); ++NR) ^ user.cpp:77:39: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("poligon5.in", "r", stdin); ^ user.cpp:78:41: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("poligon5.out", "w", stdout); ^ user.cpp:79:24: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] for(scanf("%d", &T); T > 0; --T){ ^ user.cpp:80:24: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d", &n); ^ user.cpp:84:35: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d %d", &A, &B); ^