using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Threading.Tasks;

using System.Collections;  

public class Program

{

    class Student

    {

        public int StudentID { get; set; }

        public String StudentName { get; set; }

    }

    public static void Main()

    {

        IList mixedList = new ArrayList();

        mixedList.Add(0);

        mixedList.Add("One");

        mixedList.Add("Two");

        mixedList.Add(3);

        mixedList.Add(new Student() { StudentID = 1, StudentName = "Bill" });

​

        var stringResult = from s in mixedList.OfType<string>()

                           select s;

​

        var intResult = from s in mixedList.OfType<int>()

                        select s;

​

        var stdResult = from s in mixedList.OfType<Student>()

                        select s;

​

        foreach (var str in stringResult)       

            Console.WriteLine(str);

​

        foreach (var integer in intResult)

            Console.WriteLine(integer);

        foreach (var std in stdResult)

            Console.WriteLine(std.StudentName);     

​

    }

}