tic-tac-toe.cpp

// 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);
}