/in/foo.cc: In function 'int main(int, char**)':
/in/foo.cc:47:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (i = 0; i < vtSet_C.size(); i++)
              ~~^~~~~~~~~~~~~~~~
/in/foo.cc: In function 'void DifferenceSet(std::vector<int>, std::vector<int>, std::vector<int>*)':
/in/foo.cc:57:17: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for (i = 0; i < vtSet_A.size(); i++)
               ~~^~~~~~~~~~~~~~~~
/in/foo.cc:60:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    for (j = 0; j < vtSet_B.size(); j++)
                ~~^~~~~~~~~~~~~~~~