53abstractbaseclass.cpp

/*
ABSTRACT BASE CLASS, WHAT IS IT?

ANS :- A CODE USING CLASSES WHICH HAS ATLEAST ONE PURE VIRTUAL FUNCTION IN A BASE CLASS, THAT CLASS IS CALLED AN
        "ABSTRACT BASE CLASS".

        What is a pure virtual function? 
        ans :- below 
*/

#include <iostream>
using namespace std;

class a
{
protected:
    int x;

public:
    a() : x(4) {}
    /*virtual void display() {}*/ 
    // When this is activated, in the absence of derived function this will be fetched

    //PURE VIRTUAL FUNCTION
    virtual void display() = 0;
    // When this is activated, in the absence of derived function, it will throw error as this is a "pure virtual function" and is never involved
};

class b : public a{
    int y;
    public:
    b() : y(3){}
    void display() 
    {
        cout<<"Derived class, data a and b "<<x<<" and "<<y<<endl;
    }
};
int main()
{
    a * ptr;
    b obj;
    ptr = &obj;
    ptr->display();
    return 0;
}