Compilare: user.cpp: In function ‘int main()’: user.cpp:50:29: warning: format ‘%lu’ expects argument of type ‘long unsigned int’, but argument 2 has type ‘std::vector<std::vector<int> >::size_type {aka unsigned int}’ [-Wformat=] printf("%lu\n", ans.size()); ^ user.cpp:51:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(i=0;i<ans.size();i++) { ^ user.cpp:52:32: warning: format ‘%lu’ expects argument of type ‘long unsigned int’, but argument 2 has type ‘std::vector<int>::size_type {aka unsigned int}’ [-Wformat=] printf("%lu", ans[i].size()); ^ user.cpp:53:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(j=0;j<ans[i].size();j++) { ^ user.cpp:25:31: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("dubi.in","r",stdin); ^ user.cpp:26:33: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("dubi.out","w",stdout); ^ user.cpp:34:18: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d", &n); ^