using System;

using System.Collections.Generic;

using System.Linq;

​

public class Program

{

    public static void Main()

    {

        //

        // This List has three elements.

        //

        var list = new List<string>() { "Cat", "Rat", "Mouse" };

        Console.WriteLine(list.FirstOrDefault());

​

        //

        // This query produces no results so FirstOrDefault is null.

        //

        var query1 = from element in list

                    where element.Length > 10

                    select element;

        //Console.WriteLine(query1.FirstOrDefault() == null);

​

        //

        // This query produces one result, so FirstOrDefault is a string.

        //

        var query2 = from element in list

                     where element.Length > 3

                     select element;

        //Console.WriteLine(query2.FirstOrDefault());

​

        //

        // This array has no elements, so FirstOrDefault is zero.

        //

        int[] array = new int[0];

        //Console.WriteLine(array.FirstOrDefault());

    }

}