using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        IList<int> intList = new List<int>() { 10, 21, 30, 45, 50, 87 };

        var total = intList.Sum();

        Console.WriteLine("Sum: {0}", total);

        Console.WriteLine();

        var sumOfEvenElements = intList.Sum(i => { if(i%2 == 0) return i; return 0;});

        Console.WriteLine("Sum of even elements: {0}", sumOfEvenElements);

        Console.WriteLine();

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

        { 

            new Student() { StudentID = 1, StudentName = "John", Age = 13} ,

            new Student() { StudentID = 2, StudentName = "Moin",  Age = 21 } ,

            new Student() { StudentID = 3, StudentName = "Bill",  Age = 18 } ,

            new Student() { StudentID = 4, StudentName = "Ram" , Age = 20} ,

            new Student() { StudentID = 5, StudentName = "Ron" , Age = 15 } 

        };

        var sumOfAge = studentList.Sum(s => s.Age);

        Console.WriteLine("Students total ages {0}", sumOfAge);

        Console.WriteLine();

        var numOfAdults = studentList.Sum(s => {if (s.Age >= 18) return 1; return 0;});

        Console.WriteLine("Total Adult Students: {0}" , numOfAdults);

    }

}

​

public class Student 

{

    public int StudentID { get; set; }

    public string StudentName { get; set; }

    public int Age { get; set; }

}