Compilare: user.cpp: In function ‘int main()’: user.cpp:67:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0;i<ans.size();i++) ~^~~~~~~~~~~ user.cpp:69:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int j=0;j<ans[i].size();j++) ~^~~~~~~~~~~~~~ user.cpp:53:36: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("biconex.in","r",stdin); ^ user.cpp:54:38: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("biconex.out","w",stdout); ^ user.cpp:55:27: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d %d\n",&n,&m); ^ user.cpp:58:31: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d %d\n",&x,&y); ^