/in/foo.cc: In function 'std::vector<int> mul(std::vector<int>&, int)':
/in/foo.cc:14:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (int i = 0; i < A.size() || t; i ++ )
                  ~~^~~~~~~~~~
/in/foo.cc:16:9: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   if (i < A.size()) t += A[i] * b;
       ~~^~~~~~~~~~