C++ :: Define Virtual Function Compare In Subclass Score?

I am trying to bend my head around polymorphism but I can't figure out how to use the virtual method properly. I have the following superclass:

Code: class comparable
{
public:
comparable();
virtual bool compare(comparable &other)=0;
}; and the subclass:
Code: class score : public comparable
{
public:
score(string player,int highscore);
bool compare(comparable &other);
string name;
int highscore;
};

My problem is that I do not know how to define the virtual function compare in the subclass score:

Code: bool score::compare(comparable &other){
if(this->highscore > other.???){
...
}
}

How do I tell the compiler that the type is of score?