/in/foo.cc: In function 'std::vector<int> mul(std::vector<int>&, int, int)':
/in/foo.cc:8:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for (int i = 0; i < num.size() || carry; i++) {
                     ~~^~~~~~~~~~~~
/in/foo.cc:10:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         if (i < num.size()) {
             ~~^~~~~~~~~~~~