/in/foo.cc: In function 'void simple(int, std::__cxx11::string&)':
/in/foo.cc:39:11: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  while(len>s.length()){
        ~~~^~~~~~~~~~~
/in/foo.cc: In function 'int main()':
/in/foo.cc:50:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=1;i<b.length();i++){
              ~^~~~~~~~~~~