What is the difference between a copy constructor and an overloaded assignment operator?

class C
{
public:
C();
C(const C& c);
C& operator=(const C& c)
};

C c1; // default c-tor
C c2 = c1; // copy c-tor
C c3(c2); // copy c-tor
C c4; // default c-tor
c4 = c3; // assignment operator

A copy constructor constructs a new object by using the content of the argument object. An overloaded assignment operator assigns the contents of an existing object to another existing object of the same class.