prog.cpp: In member function 'X& X::operator=(const X&)':
prog.cpp:2:1: error: non-static reference member 'int& X::r', can't use default assignment operator
prog.cpp: In function 'int main()':
prog.cpp:11:9: note: synthesized method 'X& X::operator=(const X&)' first required here
prog.cpp:12:5: error: 'cout' is not a member of 'std'