/in/foo.cc: In function 'int get(std::__cxx11::string)':
/in/foo.cc:56:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=4;i<ss.length();i++){
              ~^~~~~~~~~~~~
/in/foo.cc: In function 'int getf(std::__cxx11::string)':
/in/foo.cc:65:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=4;i<ss.length();i++){
              ~^~~~~~~~~~~~
/in/foo.cc:72:17: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=pos;i<ss.length();i++) 
                ~^~~~~~~~~~~~
/in/foo.cc: In function 'void check_n()':
/in/foo.cc:190:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=4;i<qwq.length()-1;i++) book=book*10+(qwq[i]-'0');
              ~^~~~~~~~~~~~~~~