/in/foo.cc: In function 'std::vector<int> mul(std::vector<int>&, int)':
/in/foo.cc:10:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for (int i = 0; i < a.size() || t; i++)
                     ~~^~~~~~~~~~
/in/foo.cc:12:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         if (i < a.size()) t += a[i] * b;
             ~~^~~~~~~~~~
/in/foo.cc: In function 'int main()':
/in/foo.cc:31:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for (int i = 0; i < a.size(); i++)
                     ~~^~~~~~~~~~