using System;

public class Program

{

    public static void Main()

    {

        /* Foo is null */

        string foo = null;

        string bar = "Bar";

        bar = foo ?? bar;

        Console.WriteLine(bar); //bar remains 'Bar', as foo was null

        /* Foo is not null */

        foo = "Foo";

        bar = "Bar";

        bar = foo ?? bar;

        Console.WriteLine(bar); //bar is 'Foo', as foo was NOT null

    }

}