/in/foo.cc: In function 'int main()':
/in/foo.cc:14:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (int i = 0; i < s.size(); i++)
                  ~~^~~~~~~~~~
/in/foo.cc:22:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (int i = 0; i < qs.size(); i++)
                  ~~^~~~~~~~~~~
/in/foo.cc:26:25: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for (int j = i + 1; j < qs.size();j++)
                       ~~^~~~~~~~~~~