Member initializer list program in C++

/*C++ program to demonstrate example of member initializer list.*/
#include <iostream>
using namespace std;
 
//Class declaration.
class Demo
{
    //Private block  to declare data member( X,Y ) of integer type.
    private:
        const int X;
        const int Y;
 
    //Public block of member function to access data members.
    public:
        //Const member can only be initialized with member initializer list.
        //Declaration of defalut constructor.
            Demo():X(10),Y(20){};
        //Declaration of parameterized constructor to initialize data members by member intializer list.
            Demo (int a, int b) : X(a),Y(b){}; 
        //To display output onn screen.
        void    Display();
     
};//End of class
 
 
//Definition of Display() member function.
void Demo:: Display()
{
    cout << endl << "X: " << X;
    cout << endl << "Y: " << Y << endl;
}
 
int main()
{
    //Ctor automatically call when object is created.
    Demo d1; //Default constructor
    Demo d2(30,40) ; //Parameterized constructor.
 
    //Display value of data member.
    cout << "Value of d1: " ;
    d1.Display();   
 
    cout << "Value of d2: ";
    d2.Display();   
     
    return 0;
}

Output

    Value of d1: 
    X: 10
    Y: 20
    Value of d2: 
    X: 30
    Y: 40