using System;

​

public class Program

{

    public static void Main()

    {

        var foo = new Foo();

        // access a value    

        string berlin = foo[2];

        // assign a value

        foo[0] = "Rome";

        Console.WriteLine(foo[0]);

    }

}

​

class Foo

{

    private string[] cities = new[]

    {

    "Paris", "London", "Berlin"

    };

    public string this[int index]

    {

        get

        {

            return cities[index];

        }

​

        set

        {

            cities[index] = value;

        }

    }

}