/in/foo.cc: In function 'int main()':
/in/foo.cc:13:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0;i<s.size();++i){
               ^
/in/foo.cc:9:5: warning: unused variable 'n' [-Wunused-variable]
 int n;
     ^