/in/foo.cc: In function 'int main()':
/in/foo.cc:13:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for(int i=0; i<s.size(); i++)
                      ~^~~~~~~~~
/in/foo.cc:17:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for(int j=0; j<s.size(); j++)
                      ~^~~~~~~~~
/in/foo.cc:48:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for(int j=0; j<s1.size(); j++)
                      ~^~~~~~~~~~
/in/foo.cc:57:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for(int j=0; j<s1.size(); j++)
                      ~^~~~~~~~~~