/in/foo.cc: In function 'std::__cxx11::string fr(std::__cxx11::string)':
/in/foo.cc:10:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i = 0;i < n.size();i++){
                ~~^~~~~~~~~~
/in/foo.cc: In function 'std::__cxx11::string ba(std::__cxx11::string)':
/in/foo.cc:19:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i = 0;i < n.size();i++){
                ~~^~~~~~~~~~