Having fun with custom collections!

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ListTUsage
{
	class Program
	{
		static void Main(string[] args)
		{
			// Create a new list and add some numbers to it.
			List<int> list = new List<int>();
			list.Add(4);
			list.Add(1);
			list.Add(44);
			list.Add(3);
			list.Add(5);
			list.Add(20);
			list.Add(10);

			Console.WriteLine("All Integers in the list.");
			Console.WriteLine(GetNumbersAsString(list));

			Console.WriteLine();
			Console.WriteLine("Add a 3 if it is not already in the list and show all Integers again.");
			// Contains will return a Boolean saying if the provided Object is already in the list.
			if (!list.Contains(3))
			{
				Console.WriteLine("A 3 was added to the list.");
				list.Add(3);
			}
			else
			{
				Console.WriteLine("A 3 was not added to the list.");
			}
			Console.WriteLine(GetNumbersAsString(list));

			Console.WriteLine();
			Console.WriteLine("Add a 3 and show all Integers again.");
			// Doubles are allowed.
			list.Add(3);
			Console.WriteLine(GetNumbersAsString(list));

			Console.WriteLine();
			Console.WriteLine("Sort the list and show all Integers again.");
			// Sort the list.
			list.Sort();
			Console.WriteLine(GetNumbersAsString(list));

			Console.WriteLine();
			Console.WriteLine("Reverse the list and show all Integers again.");
			// Reverse the list.
			list.Reverse();
			Console.WriteLine(GetNumbersAsString(list));

			Console.WriteLine();
			Console.WriteLine("Remove a 4 from the list and show all Integers again.");
			// Remove a 4 from the list. If it succeeds this Function returns True.
			if (list.Remove(4))
			{
				Console.WriteLine("A 4 was successfully removed from the list.");
			}
			else
			{
				Console.WriteLine("A 4 could not be removed from the list.");
			}
			Console.WriteLine(GetNumbersAsString(list));

			Console.WriteLine();
			Console.WriteLine("Remove another 4 from the list and show all Integers again.");
			// Remove a 4 from the list. If it succeeds this Function returns True.
			if (list.Remove(4))
			{
				Console.WriteLine("Another 4 was successfully removed from the list.");
			}
			else
			{
				Console.WriteLine("Another 4 could not be removed from the list.");
			}
			Console.WriteLine(GetNumbersAsString(list));

			Console.WriteLine();
			Console.WriteLine("Create a new list and give it all items from the old list.");
			// The constructor has two overloads, one that accepts an Integer that will set the
			// initial size of the list (List<T> still uses an Array internally).
			// The other one accepts another collection as argument.
			// This will create a new list containing all of the elements from the passed list.
			List<int> list2 = new List<int>(list);
			Console.WriteLine(GetNumbersAsString(list2));

			Console.WriteLine();
			Console.WriteLine("This concludes the brief introduction to the List<T> Class.");

			Console.ReadKey();
		}

		private static string GetNumbersAsString(List<int> list)
		{
			string s = string.Empty;
			foreach (int i in list)
			{
				s += i + ", ";
			}
			// Delete the last comma.
			return s.Substring(0, s.Length - 2);
		}
	}
}