MY CODE >> Hexadecimal Calculator
/* Tommy Martin
 * 11/14/2012
 * 
 * This Program Coverts Hexadecimal Numbers to Decimal Numbers
 * 
 * Program.cs
 */

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

namespace HexadecimalToDecimal
{
    class Program
    {
        static void Main(string[] args)
        {

            string hex = Console.ReadLine();
            char[] hexChar = hex.ToCharArray();

            int power = 0;
            double total = 0;
            bool checkHex = false;
            for (int x = hexChar.Length - 1; x >= 0; x--)
            {

                switch (hexChar[x])
                {

                    case '0': total += Math.Pow(16, power) * 0;
                        break;
                    case '1': total += Math.Pow(16, power) * 1;
                        break;
                    case '2': total += Math.Pow(16, power) * 2;
                        break;
                    case '3': total += Math.Pow(16, power) * 3;
                        break;
                    case '4': total += Math.Pow(16, power) * 4;
                        break;
                    case '5': total += Math.Pow(16, power) * 5;
                        break;
                    case '6': total += Math.Pow(16, power) * 6;
                        break;
                    case '7': total += Math.Pow(16, power) * 7;
                        break;
                    case '8': total += Math.Pow(16, power) * 8;
                        break;
                    case '9': total += Math.Pow(16, power) * 9;
                        break;
                    case 'a':
                    case 'A': total += Math.Pow(16, power) * 10;
                        break;
                    case 'b':
                    case 'B': total += Math.Pow(16, power) * 11;
                        break;
                    case 'c':
                    case 'C': total += Math.Pow(16, power) * 12;
                        break;
                    case 'd':
                    case 'D': total += Math.Pow(16, power) * 13;
                        break;
                    case 'e':
                    case 'E': total += Math.Pow(16, power) * 14;
                        break;
                    case 'f':
                    case 'F': total += Math.Pow(16, power) * 15;
                        break;

                    default: Console.WriteLine("Error computing... Please enter a Hexadecimal Number.");
                             Console.WriteLine("Each digit must be either 0-9 or A-F");
                        checkHex = true;
                        break;
                }

                if (checkHex)
                    x = -1;
                power++;

            }

            if(!checkHex)
                Console.WriteLine("Total is: {0}", total);

            Console.ReadLine();

        }
    }
}