README.md

// 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); 

}