foo.cc: In member function ‘int PolyListArray::Sum()’:
foo.cc:78:34: error: cannot bind non-const lvalue reference of type ‘PolyList&’ to an rvalue of type ‘PolyList’
   78 |                         tem=(tem + p[i]);
      |                             ~~~~~^~~~~~~
foo.cc:30:39: note:   initializing argument 1 of ‘PolyList PolyList::operator=(PolyList&)’
   30 |         PolyList operator = (PolyList&p)
      |                              ~~~~~~~~~^