Compilare: user.cpp: In member function ‘bool Comp::operator()(const std::pair<int, int>&, const std::pair<int, int>&) const’: user.cpp:16:23: warning: statement has no effect [-Wunused-value] else A.second < B.second; ^ user.cpp: In function ‘int main()’: user.cpp:51:35: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int j = 0; j < V.size(); ++ j) printf("%i ", V[j].second); ^ user.cpp: In member function ‘bool Comp::operator()(const std::pair<int, int>&, const std::pair<int, int>&) const’: user.cpp:17:5: warning: control reaches end of non-void function [-Wreturn-type] } ^