/in/foo.cc: In function 'int main()':
/in/foo.cc:11:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0;i<s1.size();i++)
              ~^~~~~~~~~~
/in/foo.cc:14:12: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(j=0;j<s2.size();j++)
           ~^~~~~~~~~~
/in/foo.cc:23:7: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   if(j==s2.size())s++;
      ~^~~~~~~~~~~