foo.cc: In member function 'PolyListNode& PolyListNode::operator=(PolyListNode&)':
foo.cc:16:77: warning: no return statement in function returning non-void [-Wreturn-type]
   16 |  PolyListNode & operator = (PolyListNode &x){ coe = x.coe; index = x.index; }
      |                                                                             ^
      |                                                                             return *this;
foo.cc: In constructor 'PolyList::PolyList(int)':
foo.cc:25:6: warning: 'PolyList::n' will be initialized after [-Wreorder]
   25 |  int n;    //数量
      |      ^
foo.cc:24:6: warning:   'int PolyList::size' [-Wreorder]
   24 |  int size;   //有效范围
      |      ^~~~
foo.cc:27:2: warning:   when initialized here [-Wreorder]
   27 |  PolyList(int n = 0):n(n),size(1){ a =new PolyListNode[size]; }
      |  ^~~~~~~~

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