gistfile1.cs

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

namespace ConsoleApplication1
{
	interface IItem
	{
		string Name { get; }
	}

	interface IUsable : IItem
	{
		void Use();
	}

	interface IExaminable : IItem
	{
		void Examine();
	}

	abstract class Key : IItem, IUsable, IExaminable
	{
		public string Name { get; private set; }

		public Key(string name)
		{
			Name = name;
		}

		public abstract void Use();

		public void Examine()
		{
			Console.WriteLine("Looking at a key!");
		}
	}

	class RedKey : Key
	{
		public RedKey()
			: base("Red")
		{
		}

		public override void Use()
		{
			Console.WriteLine("Unlocking red doors");
		}
	}

	class GreenKey : Key
	{
		public GreenKey()
			: base("Green")
		{
		}

		public override void Use()
		{
			Console.WriteLine("Unlocking green doors");
		}
	}

	class Mural : IItem, IExaminable
	{
		public string Name { get; private set; }

		public Mural(string name)
		{
			Name = name;
		}

		public void Examine()
		{
			Console.WriteLine("Looking at a mural!");
		}
	}

	class Program
	{
		static void Main(string[] args)
		{
			var inventory = new List<IItem> 
			{
				new RedKey(),
				new GreenKey(),
				new Mural("Whoa"),
				new Mural("Hey There!"),
			};

			while (true)
			{
				Console.Clear();
				Console.WriteLine("INVENTORY:");
				for (var i = 0; i < inventory.Count; i++)
				{
					Console.WriteLine("[{0}] - {1}", i + 1, inventory[i].Name);
				}

				var input = Console.ReadLine();
				var parts = input.Split(' ');
				if (parts.Length == 2)
				{
					int itemIndex;
					if (!int.TryParse(parts[1], out itemIndex))
						continue;

					if (itemIndex <= 0 || itemIndex > inventory.Count)
						continue;

					var item = inventory[itemIndex - 1];

					if (parts[0] == "use")
					{
						var useable = item as IUsable;
						if (useable != null)
							useable.Use();
						else
							Console.WriteLine("{0} is not useable!", item.Name);
					}

					if (parts[0] == "examine")
					{
						var examineable = item as IExaminable;
						if (examineable != null)
							examineable.Examine();
						else
							Console.WriteLine("{0} is not examinable!", item.Name);
					}
				}

				Console.WriteLine("Press any key");
				Console.ReadKey();
			}

			Console.ReadKey();
		}
	}
}