/in/foo.cc: In function 'void Add(std::vector<Poly>&, std::vector<Poly>)':
/in/foo.cc:41:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0; i<L2.size(); i++)
               ~^~~~~~~~~~
/in/foo.cc: In function 'void Output(std::vector<Poly>)':
/in/foo.cc:48:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0; i<L.size()&&L[i].coef!=0; i++)
               ~^~~~~~~~~
/in/foo.cc: In function 'int main()':
/in/foo.cc:66:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0;i<L1.size();i++)
              ~^~~~~~~~~~
/in/foo.cc:67:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(int j=0;j<L2.size();j++)
               ~^~~~~~~~~~