using System;

// we need this library now

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {           

        // In c# there are many useful generic types, most common is a List which makes adding and removing elements very easy

        // Declare and difine

        List<string> lista = new List<string>();

        // Add elements

        lista.Add("a1");

        lista.Add("b4");                

        lista.Add("c4");

        lista.Add("d0");

        lista.Remove("b4");

        foreach (var item in lista)

        {

            Console.Write($"{item},");

        }

        Console.WriteLine();

        // Another useful one i a HashSet, that will make sure, all elements are unique

        // Declare and difine

        HashSet<int> hash = new HashSet<int>();

        // Add elements

        hash.Add(3);

        hash.Add(2);

        hash.Add(5);        

        hash.Add(2);

        foreach (var item in hash)

        {

            Console.Write($"{item},");

        }

        Console.WriteLine();

        // There is also a dictionary

        // Declare and difine

        Dictionary<int, string> dict = new Dictionary<int, string>();

        // Add elements

        dict.Add(1, "red");     

        dict.Add(2, "orange");

        dict.Add(3, "blue");

        foreach (var item in dict.Values)

        {

            Console.Write($"{item},");

        }

        // Element at key

        // foreach entry, key and value

    }

}