L33tspeaktranslator.cs

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

namespace CodeADay
{
    class Program
    {
        private static Dictionary<string, string> CharacterMappings = new Dictionary<string, string>();

        static void ConvertToLeet(ref string text)
        {
            text = text.ToUpper();

            foreach (KeyValuePair<string, string> characterMap in CharacterMappings)
            {
                text = text.Replace(characterMap.Key, characterMap.Value);
            }
        }

        static void ConvertFromLeet(ref string text)
        {
            foreach (KeyValuePair<string, string> characterMap in CharacterMappings)
            {
                text = text.Replace(characterMap.Value, characterMap.Key).ToLower();
            }
        }

        static void Main(string[] args)
        {
            CharacterMappings.Add("A", "4");
            CharacterMappings.Add("B", "6");
            CharacterMappings.Add("E", "3");
            CharacterMappings.Add("I", "1");
            CharacterMappings.Add("L", "|");
            CharacterMappings.Add("M", "(V)");
            CharacterMappings.Add("N", @"(\)");
            CharacterMappings.Add("O", "0");
            CharacterMappings.Add("S", "5");
            CharacterMappings.Add("T", "7");
            CharacterMappings.Add("V", @"\/");
            CharacterMappings.Add("W", "`//");

            bool loop = true;
            while (loop)
            {
                string mode = "0";

                while (mode != "1" || mode != "2")
                {
                    Console.Write("Convert to leet (enter 1) or from leet (enter 2): ");
                    mode = Console.ReadLine();
                } 
                
                if (mode == "1")
                {
                    Console.Write("Please enter some text to translate:");
                    string text = Console.ReadLine();
                    ConvertToLeet(ref text);
                    Console.WriteLine("-> {0}", text);
                }
                else if (mode == "2")
                {
                    Console.Write("Please enter some text to translate:");
                    string text = Console.ReadLine();
                    ConvertFromLeet(ref text);
                    Console.WriteLine("-> {0}", text);
                }

                Console.Write("Would you like to continue? Y/N: ");
                string cont = Console.ReadLine();

                if (cont.ToUpper() == "N")
                {
                    loop = false;
                }
            }
        }
    }
}