/in/foo.cc: In function 'void Output(std::vector<Student>&)':
/in/foo.cc:23:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0; i<ss.size(); i++)
               ~^~~~~~~~~~
/in/foo.cc: In function 'int main()':
/in/foo.cc:42:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0; i<ss.size(); i++)
               ~^~~~~~~~~~
/in/foo.cc:44:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=1; i<ss.size(); i++)
               ~^~~~~~~~~~