/in/foo.cc: In function 'void PrimeCount(std::vector<int>, std::vector<int>)':
/in/foo.cc:25:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for (int i = 0; i < a.size(); i++)
                     ~~^~~~~~~~~~
/in/foo.cc:33:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for (int i = 0; i < b.size(); i++)
                     ~~^~~~~~~~~~