/in/foo.cc: In function 'int countdifk(std::__cxx11::string, int)':
/in/foo.cc:25:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (int i = 0; i < s.length(); i++)
                  ~~^~~~~~~~~~~~
/in/foo.cc:29:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for (int j = i; j < s.length(); j++)
                   ~~^~~~~~~~~~~~