/in/foo.cc: In function 'int main()':
/in/foo.cc:15:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(int i=0;i<s.size()-2;i++)
               ~^~~~~~~~~~~
/in/foo.cc:21:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(int i=0;i<s.size()-3;i++)  
               ~^~~~~~~~~~~