/in/foo.cc: In member function 'void PolyList::Select()':
/in/foo.cc:23:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(int i=0;i<x.size();i++)
               ~^~~~~~~~~
/in/foo.cc:26:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    for(int j=i+1;j<x.size();j++)
                  ~^~~~~~~~~
/in/foo.cc: In member function 'void PolyList::Output()':
/in/foo.cc:65:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(int i=0;i<x.size();i++)
               ~^~~~~~~~~