How to properly implement cheat codes?

Question

what would be the best way to implement kind of cheat codes in general? I have WinForms application in mind, where a cheat code would unlock an easter egg, but the implementation details are not relevant.

The best approach that comes to my mind is to keep index for each code - let's consider famous DOOM codes - IDDQD and IDKFA, in a fictional C# app.

string[] CheatCodes = { "IDDQD", "IDKFA"};
int[] CheatIndexes = { 0, 0 };
const int CHEAT_COUNT = 2;
void KeyPress(char c)
{
    for (int i = 0; i < CHEAT_COUNT; i++) //for each cheat code
    {
        if (CheatCodes[i][CheatIndexes[i]] == c)
        { //we have hit the next key in sequence
            if (++CheatIndexes[i] == CheatCodes[i].Length) //are we in the end?
            {
                //Do cheat work
                MessageBox.Show(CheatCodes[i]);
                //reset cheat index so we can enter it next time
                CheatIndexes[i] = 0; 
            }
        }
        else //mistyped, reset cheat index
            CheatIndexes[i] = 0; 
    }
}

Is this the right way to do it?

Edit: Probably the worst thing I should have done was to include the first cheat codes that came from the top of my head as an example. I really did not want to see Doom's source code or their implementation, but general solution to this problem.

Answer 1

Why not download the DOOM source and see for yourself? =) http://www.doomworld.com/idgames/?id=14576

Answer 2

I think this one's a bit easier to understand, though your original will probably perform better than this one:

using System.Collections.Generic;

void KeyPress(char c)
{
    string[] cheatCodes = { "IDDQD", "IDKFA"};
    static Queue<char> buffer; //Contains the longest number of characters needed
    buffer.Enqueue(c);
    if (buffer.Count() > 5) //Replace 5 with whatever your longest cheat code is
        buffer.Dequeue();
    bufferString = new System.String(buffer.ToArray());
    foreach(string code in cheatCodes) {
        if (bufferString.EndsWith(code)) {
            //Do cheat work
        }
    }
}