Contents

Contents of help

Rules of the game

Making a move

Technical information

The menu commands

The status bar

About


Rules

Rules of the Game

The players take turns in making their move, which is dropping a stone of their color (yellow for the one who starts) down one of the columns which are numbered 1 to 7. The first player to get four (or more) stones in either a vertical, horizontal or diagonal row wins the game.

The game belongs to the two-person full information class of board games (other examples include tic-tac-toe, reversi and chess), which means that, assuming both players will play perfectly, the outcome of the game is already decided. In the case of connect four, the player to move first should win the game. This result was derived with the aid of computers by James D. Allen and Victor Allis independently. This program does not play perfectly, however, there is a DOS program which will play perfectly with the aid of a opening book of 60'000 moves. You can download it at http://aida.eng.unipr.it/~gbe/velena.html.


Making a move

You make a move by simply clicking in the column where you wish to drop the stone. If you made a mistake and would like to take back your move, press t twice when it's your move again. If you would like to not only make a move, but also a good move, you could read an article on expert connect four playing: http://daisy.uwaterloo.ca/~tromp/c4.html.


Technical information

This program uses some standard techniques of game playing software:

alpha-beta algorithm

quiescence search

killer move prediction

hashtable

opening book

The hashtable has a fixed size of about 2 MBytes, which corresponds to 100'000 positions. The opening book is based on literature and on calculations with this program. In some positions the program will play two different moves, to avoid repetitions.


The menu commands

Quit and New Game should be clear

Play forces the program to play instead of you, or, if the program is calculating it's next move, this command will force it to play immediatly.

Level controls how long the program will calculate for its next move:

the program will take

nearly no time on the Beginner level

about half a second on the Intermediate level

about five seconds on the Expert level and

about one minute on The Master level

Select determines how often the program will be allowed to increase the search depth if it believes the position to be promising. I recommend not to use the selective search. In positions where there is an immediate tactical win, a nonzero select value usually shortens the time the program takes to find the win.

Book turns the opening book on and off.


Information in the status bar

The status bar

In the status bar you will find information about the search depth,the program's evaluation of the position, the number of positions searched and the time taken. You will also see if the move is in the opening book of the program. The information on the search depth has the format d1/d2, where d1 is the depth up to which the game tree has been exhaustively searched, d2 is the maximum depth reached in forced variations. The value of the position is positive if the program believes the position to be good for itself. Values of about 200 indicate that the program has a winning threat, values of 400 indicate that the program has a double threat, usually leading to a quick win. Values of about 5000 indicate that the program has seen a forced win.


About this program

About Connect 4 for Windows 95

Connect 4 for Windows 95 v 1.01

Written by Martin Fierz 1996

Thanks to Andri Schaufelbuehl and Bernhard Seybold

Comments, Questions, Postcards, Money & Marriage Proposals to

Martin Fierz, Gladbachstr. 118, 8044 Zuerich, Switzerland

email: mafierz@ibm.net