using System;

using System.Collections;

using System.Collections.Generic;

using System.Linq;

using System.Linq.Expressions;

​

public class Student

{

    public int StudentID

    {

        get;

        set;

    }

​

    public string StudentName

    {

        get;

        set;

    }

​

    public int Age

    {

        get;

        set;

    }

}

​

public static class EnumerableExtensionMethods

{

    public static IEnumerable<Student> GetTeenAgerStudents(this IEnumerable<Student> source)

    {

        //IList<Student> s = new List<Student>();

        foreach (Student std in source)

        {

            Console.WriteLine("Accessing student {0}", std.StudentName);

            if (std.Age > 12 && std.Age < 20)

                yield return std;

                //s.Add(std);

        }

        //return s;

    }

}

​

public class Program

{

    public static void Main()

    {

        IList<Student> studentList = new List<Student>()

        {

        new Student()

        {

        StudentID = 1, StudentName = "John", Age = 13

        }

​

        , new Student()

        {

        StudentID = 2, StudentName = "Steve", Age = 15

        }

​

        , new Student()

        {

        StudentID = 3, StudentName = "Bill", Age = 18

        }

​

        , new Student()

        {

        StudentID = 4, StudentName = "Ram", Age = 12

        }

​

        , new Student()

        {

        StudentID = 5, StudentName = "Ron", Age = 21

        }

        }

​

        ;

        var teenAgerStudents =

            from s in studentList.GetTeenAgerStudents()select s;

        studentList.Add(new Student(){StudentID = 6, StudentName = "Tayo", Age = 15});

        foreach (Student teenStudent in teenAgerStudents)

            Console.WriteLine("Student Name: {0}", teenStudent.StudentName);

    }

}