/in/foo.cc: In function 'int main()':
/in/foo.cc:11:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (i = 0; i < s.length(); i++) {
              ~~^~~~~~~~~~~~
/in/foo.cc:13:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for (j = i + 1; j < s.length(); j++) {
                   ~~^~~~~~~~~~~~
/in/foo.cc:26:10: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   if ((j == s.length()&& k==-1) && !success)
        ~~^~~~~~~~~~~~~