pure virtual functions in c++

#include<iostream>
using namespace std;

class Base
{
int x;
public:
virtual void fun() = 0;
int getX() { return x; }
};

// This class inherits from Base and implements fun()
class Derived: public Base
{
int y;
public:
void fun() { cout << "fun() called"; }
};

int main(void)
{
Derived d;
d.fun();
return 0;
}