/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<s.size();i++)
              ~^~~~~~~~~
/in/foo.cc:15:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(int i=0;i<t.size();i++)
               ~^~~~~~~~~