/in/foo.cc: In member function 'Bigint Bigint::operator*(Bigint)':
/in/foo.cc:29:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for (int i = 0; i < v.size(); i++)
                         ~~^~~~~~~~~~
/in/foo.cc:30:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
             for (int j = 0; j < x.v.size(); j++)
                             ~~^~~~~~~~~~~~
/in/foo.cc:32:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for (int i = 0; i < v.size() * x.v.size(); i++)
                         ~~^~~~~~~~~~~~~~~~~~~~~~~