/in/foo.cc: In function 'bool cmp(std::__cxx11::string, std::__cxx11::string)':
/in/foo.cc:7:25: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(register int i=0; i<min(a.length(),b.length()); i++) {
                        ~^~~~~~~~~~~~~~~~~~~~~~~~~~~
/in/foo.cc: In function 'std::__cxx11::string sor(std::__cxx11::string)':
/in/foo.cc:16:25: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(register int i=0; i<a.length(); i++) {
                        ~^~~~~~~~~~~