Four In A Row #1

[Home]   [Puzzles & Projects]    [Delphi Techniques]   [Math topics]   [Library]   [Utilities]




Search WWW


As of October, 2016, Embarcadero is offering a free release of Delphi (Delphi 10.1 Berlin Starter Edition ).     There are a few restrictions, but it is a welcome step toward making more programmers aware of the joys of Delphi.  They do say "Offer may be withdrawn at any time", so don't delay if you want to check it out.  Please use the feedback link to let me know if the link stops working.


Support DFF - Shop

 If you shop at Amazon anyway,  consider using this link. 


We receive a few cents from each purchase.  Thanks


Support DFF - Donate

 If you benefit from the website,  in terms of knowledge, entertainment value, or something otherwise useful, consider making a donation via PayPal  to help defray the costs.  (No PayPal account necessary to donate via credit card.)  Transaction is secure.

Mensa Daily Puzzlers

For over 15 years Mensa Page-A-Day calendars have provided several puzzles a year for my programming pleasure.  Coding "solvers" is most fun, but many programs also allow user solving, convenient for "fill in the blanks" type.  Below are Amazon  links to the two most recent years.

Mensa 365 Puzzlers  Calendar 2017

Mensa 365 Puzzlers Calendar 2018

(Hint: If you can wait, current year calendars are usually on sale in January.)


Feedback:  Send an e-mail with your comments about this program (or anything else).

Search only




Problem Description

Here is version 1 of Four-In-A-Row, also known as Connect-4, or Connect Four. It's an extended version of Tic-Tac-Toe with the winner being the first player to get 4 tokens in line, horizontally, vertically, or diagonally.  

The game is normally played on a board that is 7 columns wide and 6 rows high with the additional constraint that a token played in any column must occupy the lowest empty space in that column. 

This Version 1 implements Human vs. Human play; a future version will add computer play.

Background & Techniques

The mechanical version of FourInARow  typically stands upright with separators between columns so that token dropped into any column will automatically fall to the lowest open spot in that column.   This version is introduced mainly to describe the graphics and animation  framework  before we go on to explore a computerized minimax search for winning plays.   

Non-programmers are welcome to skip to the bottom of the page and  download the executable version of this Human vs. Human version.  There are, however dozens of free versions around including many online Java versions.  

Programmer's Notes:

For simplicity, there are a number of constants defined up front to define board sizes and colors.   Most of these could become user controlled variables in a future version.  

Board is defined as 2 dimensional array of integers: 0 represents an empty slot, 1 and 2 indicate that that space is occupied by players 1 and 2 respectively.   Image1 is a TImage component which holds the board image.   I chose a circular TShape component, NewChip, to represent the next token to be played.  To move, NewChip  is dragged horizontally across the top of the board image and dropped on the selected column.   Both Image1 and NewChip were dropped on a TPanel in order to simplify coordinate calculations.  (The panel is a TWindow control that is the parent of both NewChip and Image1Image1  is aligned to fill the panel, so drawing of both board and token can be referenced to (0,0) in the upper left corner.  If the advantage of that isn't clear, make version without the Panel and it will be. )  

OnMouse exits for NewChip are used to detect selecting, moving and dropping the token.   At drop time, the token is moved incrementally in a delay loop down to the lowest open position.  Once there, a circle is drawn on the image and NewChip is drawn back to it's starting position (with the other player's color of course).

Everything else is pretty straightforward:

bulletProcedure FourInARow calls procedure Match to check for 4 lined up tokens after each move.
bulletA Reset button clears the board and sets up a new game.
bullet A Random Play button makes random moves simulating the human drag and drop procedure.    
bulletI added a RetractMove button to allow users to take back moves - whether you allow its use is up to you.  Might be nice for an adult playing with  child.  (And for the programmer investigating alternative strategies. <g>)   In order to implement move retraction, we added a Moves array of points representing moves and a MoveCounts variable to count how many entries are in the array.   

Next time we'll explore the Minimax  search algorithm for this game, assuming I get it working better than it is now - I  beat the computer regularly, which I'm pretty sure is not due to my superior intelligence.   

Running/Exploring the Program 

bulletBrowse source extract
bulletDownload source
bulletDownload  executable

Suggestions for Further Explorations

While watching Random Play mode, it occurred to me that it would be interesting to make a non-animated version that would play 1000 games at a time and display cumulative statistics.  Does the 1st player have an advantage?  The longest game has 42 moves, how long is the average random game? 
Player colors and board colors and even board sizes could be controlled by the user.  (Variable board size would require converting from fixed to dynamic arrays.) 
How about 3-in-a-row, or 5-in-a-row versions?



Original:  May 05, 2002

Modified:  May 15, 2018




  [Feedback]   [Newsletters (subscribe/view)] [About me]
Copyright 2000-2018, Gary Darby    All rights reserved.