/in/foo.cc: In function 'std::vector<int> add(std::vector<int>&, std::vector<int>&)':
/in/foo.cc:63:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for (int i = 0; i < A.size(); i ++ )
                     ~~^~~~~~~~~~
/in/foo.cc:66:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         if (i < B.size())
             ~~^~~~~~~~~~
/in/foo.cc: In function 'std::vector<int> mul(std::vector<int>, int)':
/in/foo.cc:81:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(int i = 0; i < a.size(); i ++)
                    ~~^~~~~~~~~~