View Compilation Error

0_0_36947240_20891.cpp: In member function 'int Poly::operator[](int) const':
0_0_36947240_20891.cpp:86:30: error: passing 'const Poly' as 'this' argument of 'int Poly::size()' discards qualifiers [-fpermissive]
   if (idx < 0 || idx >= size())
                              ^