How to properly implement cheat codes? - keyboard

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
}
}
}

Answer 3

here is the DOOM cheat implementation from the doom source:
#define SCRAMBLE(a) \
((((a)&1)<<7) + (((a)&2)<<5) + ((a)&4) + (((a)&8)<<1) \
+ (((a)&16)>>1) + ((a)&32) + (((a)&64)>>5) + (((a)&128)>>7))
int cht_CheckCheat ( cheatseq_t* cht, char key )
{
int i;
int rc = 0;
if (firsttime)
{
firsttime = 0;
for (i=0;i<256;i++) cheat_xlate_table[i] = SCRAMBLE(i);
}
if (!cht->p)
cht->p = cht->sequence; // initialize if first time
if (*cht->p == 0)
*(cht->p++) = key;
else if
(cheat_xlate_table[(unsigned char)key] == *cht->p) cht->p++;
else
cht->p = cht->sequence;
if (*cht->p == 1)
cht->p++;
else if (*cht->p == 0xff) // end of sequence character
{
cht->p = cht->sequence;
rc = 1;
}
return rc;
}