using System;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        // a is null, coalescing will display the non-null value.

        int? A = null;      

        Console.WriteLine(A ?? 0);

        // now a is NOT null, coalesce will use the value of a

        A = 1;

        Console.WriteLine(A ?? 0);

    }

}