/in/foo.cc: In function 'void Output(std::vector<student>&)':
/in/foo.cc:44:17: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(int i=0; i<ss.size(); i++)
                ~^~~~~~~~~~
/in/foo.cc: In function 'int No(std::vector<student>&)':
/in/foo.cc:54:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0;i<ss.size();i++)
              ~^~~~~~~~~~
/in/foo.cc: In function 'bool cmp(const student&, const student&)':
/in/foo.cc:27:1: warning: control reaches end of non-void function [-Wreturn-type]
 }
 ^