/in/foo.cc: In function 'int main()':
/in/foo.cc:28:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0;i<n.size();i++){
              ~^~~~~~~~~
/in/foo.cc:29:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(int j=i+1;j<n.size();j++){
                 ~^~~~~~~~~