Compilare: main.cpp: In function 'int main()': main.cpp:37:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int k=0;k<v[j].size();k++) ~^~~~~~~~~~~~ main.cpp:18:37: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen("sortaret.in","r",stdin); ^ main.cpp:19:39: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen("sortaret.out","w",stdout); ^