Compilare: user.cpp: In function ‘std::vector<int> mul(std::vector<int>, std::vector<int>)’: user.cpp:32:26: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0;i<a.size();i++) ^ user.cpp:34:30: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int j=0;j<b.size();j++) ^ user.cpp:40:26: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0;i<r.size();i++) ^