What is the purpose of using the reserved word virtual in front of functions? If I want a child class to override a parent function, I just declare the same function such as "void draw(){}".

class Parent{ public:   void say(){ std::cout << "1"; }};
class Child : public Parent{public:void say(){ std::cout << "2"; } };
int main()
{
    Child* a = new Child();
    a->say();
    return 0;
}

The output is 2.

So again, why would the reserved word "virtual" be necessary in the header of say() ?

Thanks a bunch.