Reversi Game Board Configuration and Move Legality Checking Solution



This is the first part of a series of two labs (Lab 6 and Lab 7) that will complete an imple-mentation for a board-type game called Reversi (also called Othello). The goal of this lab is to write code that sets up the input and checks the legality of moves in this game. It makes use of two-dimensional arrays, and all of the previous material covered so far in this course, and requires some careful thinking about how to convert human-thinking into working software.

Objective: Part of the Code for a Reversi Game

The goal of this lab is to write a program that will be used (in Lab 7) as part of a Reversi game, as well as a little bit of the ‘thinking’ code that will be used in that lab to have the computer play against a human opponent.

Here is a brief description of the full Reversi game. Reversi is played on a board (like a chess board or a checkers board) that has dimensions n n, where n is even. In the picture below n = 4. The game uses tiles that are white on one side, and black on the other side (they can be “flipped” over to change their colour). One player plays white; the other player plays black. The picture below shows the initial board configuration, which has two white and two black tiles placed in advance at the centre. Observe that rows and columns are labelled with letters.

!” #” $” %”





Figure 1: Starting positions on the Reversi game board.

A “turn” consists of a player laying a tile of his/her own colour on a candidate empty board position, subject to the following two rules:

  1. There must be a continuous straight line of tile(s) of the opponent’s colour in at least one of the eight directions from the candidate empty position (North, South, East, West, and diagonals).

  1. In the position immediately following the continuous straight line mentioned in #1 above, a tile of the player’s colour must already be placed.

After playing a tile at a position that meets the above critera, all of the lines of the oppo-nent’s tiles that meet the criteria above are flipped to the player’s colour.

In the picture below, all of the candidate positions for White’s next move are shown shaded.

Note that in White’s move, two lines of Black tiles were flipped: the line directly to the

Figure 6: White responds to Black by playing at (a; c).

South, and the line to the South West.

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a turn andcasethethealternatingonlyplayer withturnsanbetweenavailablemovetheplayersisallowedresumestocontinue.Theto makegamemovesendsuntilwhena either:

move becomes available forneitheropponent. At this point, the opponent is allowed to take a

1) the entire board is full, or 2) player has an available move.

turn and the alternating turns between the players resumes. The game ends when either:

For this lab,1)theyouentirewillboardimplementisfull,or2)partneitherof theplayergamehasan-playingavailablefunctionalitymove.. You will complete

the gameForin thisLablab,7, youusingwilltheimplementfunctionalitypartoftheyougamehave-playingbuiltfunctionalityinthislab,.Yousowillpleasecompletebe mindful to build cleanthegameandin reLab-usable7,usingcodethefunctionalityforthislab!you have built in this lab, so please be mindful

to build clean and re-usable code for this lab.

For this lab, you will write a C program that will do the following: (Note that the specific

You will write a C program that will do the following: (Note that the specific details of

details of input and output will be given in the example runs below this section)

input and output will be given in the example runs below this section.)

1. The first input to the program will be n, giving the size of the n ⇥ n board. You may

1. The first input to the program will be n, giving the size of the n n board. You

assume maythatassumethesizethatofnnwillwillbe bean evennumberandwilland neverwillneverbe largerbelargerthan26, and should

declare shouldastaticdeclare2-dimensionalstatic2-dimensionalarray.Yourarray. programThereisnoshouldneedto initializeallocatememorytheboard as

dynamically or to declare variable-length arrays. Your program should initialize the

shown above and print it.

board as shown above and print it.

  1. The next sequence of inputs will describe a board configuration, representing a sit-

    1. The next sequence of inputs will describe a board configuration, representing a sit-

uation partuation-waypart-throughwaythroughagameofofReversi.. Eachlinelineof inputofinputwillconsistwillconsistofthree of three

characterscharacterswithnowithspacesnospacesin betweenin.. The firstcharacterwillwillbea becolour:acolour:BorW; theBor W; the

second character will be the row (a – z); thethird character will be the column (a –

second character will be the row (a-z); the character will be the column (a-z).

z). The three characters represent a tile of the specified colour placed at the specified

The three characters represent a tile of the specified colour placed at the specified row

row and column. The three-character sequence !!! ends the board configuration en-

and columntryphase.The.Characterthree-characterarithmetic cansequencebeused to!!!translateendsthetherows/columnsboardconfigurationintoarray entry indices, e.g. ‘b’ – ‘a’ equals 1. Note: your program should not check for move legality during this phase. This phase is simply to input an intermediate board


3. Then, your program should print a list of the available moves for the White player, followed by a list of the available moves for the Black player, given the board con-figuration input in the previous step. The available moves for each player should be printed in the order of increasing rows, then in the order of increasing columns (for available moves in the same row).

  1. Next, your program should ask the user to input a move, represented in the same three-character format. Your program should check if the move is valid, and if so, make the move, flipping the tiles correspondingly. If the move is invalid, your pro-gram should indicate so.

  1. Your program should print the final board configuration and terminate.

Your program must use the following characters to represent the state of each board posi-tion:

U – for unoccupied

B – occupied by black

W – occupied by white

For example, after the entire board above is entered, it would be printed as follows:



To print the board, your program should contain a function with the following prototype:

void printBoard(char board[][26], int n);

where board is the 2D array representing the current board state, and n is the board di-mensions.

Here is an example execution of the program:

Enter the board dimension: 4



Enter board configuration: Bba

Wca Bac



  • UUBU


Available moves for W:




Available moves for B:





Enter a move:


Valid move.



Here is another example execution of the program where the final move is invalid:

Enter the board dimension: 6



Enter board configuration: Bbd

Bad Wde Wcb





Available moves for W: ae

bc ce db ec ed

Available moves for B: ba







Enter a move:


Invalid move.



We strongly encourage you to break up your program into separate functions, and to care-fully test each function separately, before connecting it into the larger program. To help with this, you are required to create the following helper functions and use them in your implementation:

bool positionInBounds(int n, char row, char col);

which checks whether the specified (row, col) lies within the board dimensions.

It is very error prone to write separate code to check each of the eight possible line direc-tions that begin at a given tile. To simplify this, you are required to write and use the following function:

bool checkLegalInDirection(char board[][26], int n, char row, char col, char colour, int deltaRow, int deltaCol);

which checks whether (row, col) is a legal position for a tile of colour by “looking” in the direction specified by deltaRow and deltaCol. deltaRow and deltaCol take on values of -1, 0, and 1, with the restriction that they cannot both be 0. For example, if deltaRow = 1 and deltaCol = 0, the function searches the South line. If deltaRow = -1 and deltaCol = 1, the function searches the Northeast line. The idea is that, elsewhere in your program, you will call the helper function 8 times to search the lines in the 8 possible directions. The lab TAs will be checking for the presence and use of these helper functions in your program.

Write your program in a file called Lab6.c.

Grading by TA and Submitting Your Program for Auto-Marking

There are a total of 10 marks available in this lab, marked in two different ways:

  1. By your TA, for 4 marks out of 10. Once you are ready, show your program to your TA so that it can be marked for style (1 mark), and to ask you a few questions to test your understanding of what is happening (3 marks). Programs with good style have been described in previous labs, so that will not be repeated here.

  1. By an auto-marking program for 6 marks out of 10. You must submit your program file, named Lab6.c, through the ECF computers for marking as usual. Please NOTE:

7the exercise program below does not test all possible cases of input for your program, it is mainly to make sure that you are formatting your output correctly. To repeat: If your program works using the exercise program, it does not mean that you will get full marks for your program; You are responsible for testing your program using all the cases you can think of, according to the specification given in writing in this lab. Similar to the previous labs, to check the formatting of your program, you should run the following command:


within the directory that contains your solution programs.

This program will look for the file Lab6.c in your directory, compile it, and run it on some of the test cases that will be used to mark your program automatically later. If there is anything wrong, the exercise program will report this to you, so read its output carefully, and fix the errors that it reports.

  1. Once you have determined that your program is as correct as you can make it, then you must submit your program for auto-marking. This must be done by the end of your lab period as that is the due time. To do so, go into the directory containing your solution files and type the following command:


This command will re-run the exercise program to check that everything looks fine. If it finds a problem, it will ask you if you are sure that you want to submit. Note that you may submit your work as many times as you want prior to the deadline; only the most recent submission is marked.

The exercise program (and the marker program that you will run after the final dead-line) will be looking for the exact letters as described in the output in this handout, including the capitalization. When you test your program using the exercise pro-gram, you will see that it is expecting the output to be exactly this, so you will have to use it to see if you have this output correct.

Important Note: You must submit your lab by the end of your assigned lab period. Late submissions will not be accepted, and you will receive a grade of zero.

You can also check to see if what you think you have submitted is actually there, for peace of mind, using the following command:


This command will download into the directory you run it in, a copy of the file that has been submitted. If you already have a file of that same name in your directory, that file will be renamed with a number added to the end of the filename.

After the Final Deadline — Obtaining Automark

Briefly after all lab sections have finished, you will be able to run the automarker to deter-mine the automarked fraction of your grade on the code you have submitted. To do so, run the following command:


This command will compile and run your code, and test it with all of the test cases used to determine the automark grade. You will be able to see those test cases’ output and what went right or wrong.