Connect 4 AI?

I am making a connect4 clone to learn some programming.

How would I evaluate a certain position, and can I compare 7 such
evaluations to find the best move for the computer to make?

TIA

"Jonathan L." <jl@hotmail.com> wrote in message
>
> I am making a connect4 clone to learn some programming.
>
> How would I evaluate a certain position, and can I compare 7 such
> evaluations to find the best move for the computer to make?
>
You've got to know something about the game strategy. Obviously, a position
where you connect 4 scores 100, whilst a position where the opponent
connects 4 scores 0.
You might give a position where you have 2 threes (and thus will inevitably
win next round) a score of 99, unless of course the opponent also has a
three.

I don't know enough about the game to tell you how to evaluate a more normal
position, such as when opponent is forced on the next move because you have
a three, or when you have several lines of two which could develop into
fours. However the basic principle is that you score each position, and
create a tree as deep as possible of each legal move. You then play the move
that gives the best branch.
Since the number of moves is large, you won't have a particularly strong
program unless you prune the tree - avoid examining no-hoper moves. This is
quite a difficult thing to do, and of course it depends on the evaluation
function being able to distinguish between no-hoper moves and a move which
temporarily looks weak but in fact leads to a winning strategy.

On Sun, 06 Jul 2003 18:05:25 GMT, "Jonathan L." <jl@hotmail.com>
wrote:

>I am making a connect4 clone to learn some programming.
>
>How would I evaluate a certain position, and can I compare 7 such
>evaluations to find the best move for the computer to make?

This sort of thing cries out for a search tree. At first you
don't evaluate the position, you just try all legal moves. Since
there are only 7 this doesn't do too badly. At the next level you
have 7 to evaluate for each move you did in the first level, thus a
total of 49. The third level will have 343. The fourth 2401. I
suspect you can still get good response looking at the fifth at 16807
moves. (Note that it's likely that many of these branches have
already been pruned because someone won.)
If the computer wins, score 100. If the player wins, score 0.
Only at that 5th level do you even try to evaluate the position
beyondo win/loss checking. I do not have enough experience with the
game to comment on how to evaluate it.
Note that I wouldn't hardcode the depth. First, it can be used
to adjust difficulty. (I wrote a Reversi clone some time ago--I never
beat it at it's highest search depth.) Also, you might find the 6th
level at 117649 moves is viable.

Hello,

If you want to delve into this stuff, connect 4 has already been solved for
quite some time, see
http://connect4.iaw.on.ca/ and download the paper by Victor Allis. If I
recall his classes correctly he'll come up with proof-number search sooner
or later.

HTH
Mrk


"Jonathan L." <jl@hotmail.com> wrote in message
news:Xns93B070D171E65pdopdo@204.127.199.17...
> I am making a connect4 clone to learn some programming.
>
> How would I evaluate a certain position, and can I compare 7 such
> evaluations to find the best move for the computer to make?
>
> TIA