Dynamic Binding in C++

Question

Why does the derived class have to declare its methods as virtual for dynamic binding to work even though the methods of the base class are declared virtual?

Answer 1

It doesn't have to. If a method is declared virtual in a base class, overriding it in a derived class makes the overriding function virtual as well, even if the virtual keyword is not used.

Answer 2

It doesn't.

class Base
{
    virtual void foo() {}
};

class Derived : public Base
{
    void foo() {}
}

in this code foo() is still virtual in the Derived class even though it isn't declared as such.