using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        IList<string> emptyList = new List<string>();

        IList<int> emptyIntList = new List<int>();

        IList<Student> emptyStudentList = new List<Student>();

        var newList1 = emptyList.DefaultIfEmpty();

        var newList2 = emptyList.DefaultIfEmpty("None");

        var newList3 = emptyIntList.DefaultIfEmpty(100);

        var newStudentList1 = emptyStudentList.DefaultIfEmpty();

        var newStudentList2 = emptyStudentList.DefaultIfEmpty(new Student() {StudentID = 0, StudentName = "" });

        Console.WriteLine("Count: {0}", newList1.Count());

        Console.WriteLine("Value: {0}", newList1.ElementAt(0));

        Console.WriteLine("Count: {0}", newList2.Count());

        Console.WriteLine("Value: {0}", newList2.ElementAt(0));

        Console.WriteLine("Count: {0}", newList3.Count());

        Console.WriteLine("Value: {0}", newList3.ElementAt(0));

        Console.WriteLine("Count: {0}", newStudentList1.Count());

        Console.WriteLine("Student ID: {0}", newStudentList1.ElementAt(0));

        Console.WriteLine("Count: {0}", newStudentList2.Count());

        Console.WriteLine("Student ID: {0}", newStudentList2.ElementAt(0).StudentID);

    }

}

​

public class Student

{

    public int StudentID { get; set; }

    public string StudentName { get; set; }

}