/in/foo.cc: In function 'int main()':
/in/foo.cc:22:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(int i=0;i<s.size();i++)
               ~^~~~~~~~~
/in/foo.cc:24:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(int i=0;i<s.size();i++)
               ~^~~~~~~~~