Compilare: user.cpp: In function ‘std::vector<std::pair<int, int> > convex(std::vector<std::pair<int, int> >)’: user.cpp:22:29: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(i = 2; i < pts.size(); ++ i) { ^ user.cpp: In function ‘int main()’: user.cpp:54:33: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(i = 0; i < sus.size() - 1; ++ i) { ^ user.cpp:55:28: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while(j < jos.size() && ccw(sus[i], sus[i + 1], jos[j]) <= 0) ^ user.cpp:58:26: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if(j == jos.size()) { ^ user.cpp:64:33: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(i = 0; i < jos.size() - 1; ++ i) ^ user.cpp:35:24: warning: variable ‘nSus’ set but not used [-Wunused-but-set-variable] int j, iSus, iJos, nSus, nJos, x, y1, y2, n, i; ^ user.cpp:33:37: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("oypara.in", "r", stdin); ^ user.cpp:34:39: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("oypara.out", "w", stdout); ^ user.cpp:37:20: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d", &n); ^ user.cpp:40:38: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d%d%d", &x, &y1, &y2); ^ user.cpp:70:89: warning: ‘iJos’ may be used uninitialized in this function [-Wmaybe-uninitialized] printf("%d %d %d %d\n", sus[iSus].first, sus[iSus].second, jos[iJos].first, jos[iJos].second); ^ user.cpp:35:12: warning: ‘iSus’ may be used uninitialized in this function [-Wmaybe-uninitialized] int j, iSus, iJos, nSus, nJos, x, y1, y2, n, i; ^