using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Threading.Tasks;

using System.Collections;  

public class Program

{

    public static void Main()

    {

        IList<int> intList = new List<int>() { 7, 10, 21, 30, 45, 50, 87 };

        IList<string> strList = new List<string>() { "One", "Two", "Three", "Four", "Five" };

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

​

        Console.WriteLine("1st Element in intList: {0}", intList.First());

        Console.WriteLine("1st Even Element in intList: {0}", intList.First(i => i % 2 == 0));

​

        Console.WriteLine("1st Element in strList: {0}", strList.First());

​

        Console.WriteLine("emptyList.First() throws an InvalidOperationException");

        Console.WriteLine("-----------------------------------------------------");

        Console.WriteLine(emptyList.First());

    }

}