Implementation of Tic-Tac-Toe game
Rules of the Game
- The game is to be played between two people (in this program between HUMAN and COMPUTER).
- One of the player chooses ‘O’ and the other ‘X’ to mark their respective cells.
- The game starts with one of the players and the game ends when one of the players has one whole row/ column/ diagonal filled with his/her respective character (‘O’ or ‘X’).
- If no one wins, then the game is said to be draw.
Implementation
In our program the moves taken by the computer and the human are chosen randomly. We use rand() function for this.What more can be done in the program?
The program is in not played optimally by both sides because the moves are chosen randomly. The program can be easily modified so that both players play optimally (which will fall under the category of Artificial Intelligence). Also the program can be modified such that the user himself gives the input (using scanf() or cin).
The above changes are left as an exercise to the readers.Winning Strategy – An Interesting Fact
If both the players play optimally then it is destined that you will never lose (“although the match can still be drawn”). It doesn’t matter whether you play first or second.In another ways – “ Two expert players will always draw ”.
Isn’t this interesting ?// A C++ Program to play tic-tac-toe
#include<bits/stdc++.h>
using
namespace
std;
#define COMPUTER 1
#define HUMAN 2
#define SIDE 3 // Length of the board
// Computer will move with 'O'
// and human with 'X'
#define COMPUTERMOVE 'O'
#define HUMANMOVE 'X'
// A function to show the current board status
void
showBoard(
char
board[][SIDE])
{
printf
(
"\n\n"
);
printf
(
"\t\t\t %c | %c | %c \n"
, board[0][0],
board[0][1], board[0][2]);
printf
(
"\t\t\t--------------\n"
);
printf
(
"\t\t\t %c | %c | %c \n"
, board[1][0],
board[1][1], board[1][2]);
printf
(
"\t\t\t--------------\n"
);
printf
(
"\t\t\t %c | %c | %c \n\n"
, board[2][0],
board[2][1], board[2][2]);
return
;
}
// A function to show the instructions
void
showInstructions()
{
printf
(
"\t\t\t Tic-Tac-Toe\n\n"
);
printf
(
"Choose a cell numbered from 1 to 9 as below"
" and play\n\n"
);
printf
(
"\t\t\t 1 | 2 | 3 \n"
);
printf
(
"\t\t\t--------------\n"
);
printf
(
"\t\t\t 4 | 5 | 6 \n"
);
printf
(
"\t\t\t--------------\n"
);
printf
(
"\t\t\t 7 | 8 | 9 \n\n"
);
printf
(
"-\t-\t-\t-\t-\t-\t-\t-\t-\t-\n\n"
);
return
;
}
// A function to initialise the game
void
initialise(
char
board[][SIDE],
int
moves[])
{
// Initiate the random number generator so that
// the same configuration doesn't arises
srand
(
time
(NULL));
// Initially the board is empty
for
(
int
i=0; i<SIDE; i++)
{
for
(
int
j=0; j<SIDE; j++)
board[i][j] =
' '
;
}
// Fill the moves with numbers
for
(
int
i=0; i<SIDE*SIDE; i++)
moves[i] = i;
// randomise the moves
random_shuffle(moves, moves + SIDE*SIDE);
return
;
}
// A function to declare the winner of the game
void
declareWinner(
int
whoseTurn)
{
if
(whoseTurn == COMPUTER)
printf
(
"COMPUTER has won\n"
);
else
printf
(
"HUMAN has won\n"
);
return
;
}
// A function that returns true if any of the row
// is crossed with the same player's move
bool
rowCrossed(
char
board[][SIDE])
{
for
(
int
i=0; i<SIDE; i++)
{
if
(board[i][0] == board[i][1] &&
board[i][1] == board[i][2] &&
board[i][0] !=
' '
)
return
(
true
);
}
return
(
false
);
}
// A function that returns true if any of the column
// is crossed with the same player's move
bool
columnCrossed(
char
board[][SIDE])
{
for
(
int
i=0; i<SIDE; i++)
{
if
(board[0][i] == board[1][i] &&
board[1][i] == board[2][i] &&
board[0][i] !=
' '
)
return
(
true
);
}
return
(
false
);
}
// A function that returns true if any of the diagonal
// is crossed with the same player's move
bool
diagonalCrossed(
char
board[][SIDE])
{
if
(board[0][0] == board[1][1] &&
board[1][1] == board[2][2] &&
board[0][0] !=
' '
)
return
(
true
);
if
(board[0][2] == board[1][1] &&
board[1][1] == board[2][0] &&
board[0][2] !=
' '
)
return
(
true
);
return
(
false
);
}
// A function that returns true if the game is over
// else it returns a false
bool
gameOver(
char
board[][SIDE])
{
return
(rowCrossed(board) || columnCrossed(board)
|| diagonalCrossed(board) );
}
// A function to play Tic-Tac-Toe
void
playTicTacToe(
int
whoseTurn)
{
// A 3*3 Tic-Tac-Toe board for playing
char
board[SIDE][SIDE];
int
moves[SIDE*SIDE];
// Initialise the game
initialise(board, moves);
// Show the instructions before playing
showInstructions();
int
moveIndex = 0, x, y;
// Keep playing till the game is over or it is a draw
while
(gameOver(board) ==
false
&&
moveIndex != SIDE*SIDE)
{
if
(whoseTurn == COMPUTER)
{
x = moves[moveIndex] / SIDE;
y = moves[moveIndex] % SIDE;
board[x][y] = COMPUTERMOVE;
printf
(
"COMPUTER has put a %c in cell %d\n"
,
COMPUTERMOVE, moves[moveIndex]+1);
showBoard(board);
moveIndex ++;
whoseTurn = HUMAN;
}
else
if
(whoseTurn == HUMAN)
{
x = moves[moveIndex] / SIDE;
y = moves[moveIndex] % SIDE;
board[x][y] = HUMANMOVE;
printf
(
"HUMAN has put a %c in cell %d\n"
,
HUMANMOVE, moves[moveIndex]+1);
showBoard(board);
moveIndex ++;
whoseTurn = COMPUTER;
}
}
// If the game has drawn
if
(gameOver(board) ==
false
&&
moveIndex == SIDE * SIDE)
printf
(
"It's a draw\n"
);
else
{
// Toggling the user to declare the actual
// winner
if
(whoseTurn == COMPUTER)
whoseTurn = HUMAN;
else
if
(whoseTurn == HUMAN)
whoseTurn = COMPUTER;
// Declare the winner
declareWinner(whoseTurn);
}
return
;
}
// Driver program
int
main()
{
// Let us play the game with COMPUTER starting first
playTicTacToe(COMPUTER);
return
(0);
}
Output:
Tic-Tac-Toe Choose a cell numbered from 1 to 9 as below and play 1 | 2 | 3 -------------- 4 | 5 | 6 -------------- 7 | 8 | 9 - - - - - - - - - - COMPUTER has put a O in cell 6 | | -------------- | | O -------------- | | HUMAN has put a X in cell 7 | | -------------- | | O -------------- X | | COMPUTER has put a O in cell 5 | | -------------- | O | O -------------- X | | HUMAN has put a X in cell 1 X | | -------------- | O | O -------------- X | | COMPUTER has put a O in cell 9 X | | -------------- | O | O -------------- X | | O HUMAN has put a X in cell 8 X | | -------------- | O | O -------------- X | X | O COMPUTER has put a O in cell 4 X | | -------------- O | O | O -------------- X | X | O COMPUTER has won
An Interesting Variant of this game
As said above, if two experienced players are playing the Tic-Tac-Toe, then the game will always draw.
There is another viral variant of this game- Ultimate Tic-Tac-Toe, which aims to make the normal Tic-Tac-Toe more interesting and less predictable.
Have a look at the game here- Link1 Link2The above article implements simple Tic-Tac-Toe where moves are randomly made. Please refer below article to see how optimal moves are made.
Minimax Algorithm in Game Theory | Set 3 (Tic-Tac-Toe AI – Finding optimal move)Great discussions on the “winning/never losing” strategy
Quora
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