Tic-Tac-Toe#1

#define _CRT_SECURE_NO_WARNINGS

#include <iostream>
#include <vector>
#include <string>
#include <algorithm>

using namespace std;

const char X = 'X';
const char O = 'O';
const char TIE = 'T';
const char EMPTY = ' ';
const char NO_ONE = 'N';

void instructions();
void announceWinner(char winner, char& human, char& computer);
void displayBoard(const vector<char>& board);
bool isLegal(const vector<char>& board, const int& move);
int humanChoice(const vector<char>& board);
int computerChoice(vector<char>& board, const char& computer);
char detWinner(const vector<char>& board);
char choice();


int main()
{
    int move = 0;
    char computer = O; char human = X; char turn;
    const unsigned int NUM_SQUARES = 9;
    vector<char> board(NUM_SQUARES, EMPTY);
    instructions();
    turn = choice(); //returns who wil be first

    //the main cycle of game
    while (detWinner(board) == NO_ONE) //while no a winner
    {
        if (turn == human)//humans move
        {
            move = humanChoice(board);
            board[move] = human;//check a correction and returns a move
        }
        else//computers move
        {
            move = computerChoice(board, computer);
            board[move] = computer;
        }
        turn == human ? turn = computer : turn = human;
        displayBoard(board);
    }
    announceWinner(detWinner(board), human, computer);

    system("pause");
    return 0;
}

int humanChoice(const vector<char>& board)
{
    unsigned int choice;
    cout << "Your turn. Enter your choice: ";
    cin >> choice;
    if (!isLegal(board, choice))
    {
        cout << "Incorrect choice, try again.\n";
        humanChoice(board);
    }
    cout << "\nAlright..\n";
    return choice;
}

int computerChoice(vector<char>& board, const char& computer)
{
    unsigned int choice = -1;
    unsigned int move = 0;
    char human;
    const int BEST_SQUARES[] = {4, 0, 2, 6, 8, 1, 3, 5, 7};

    computer == X ? human = O : human = X;
    //if computer can win
    while (move < board.size() && choice == -1)
    {
        if (isLegal(board, move))
        {
            board[move] = computer;
            if (computer == detWinner(board))
                choice = move;
            board[move] = EMPTY;
        }
        move++;
    }

    move = 0;
    //if human can win
    while (move < board.size() && choice == -1)
    {
        if (isLegal(board, move))
        {
            board[move] = human;
            if (human == detWinner(board))
                choice = move;
            board[move] = EMPTY;
        }
        move++;
    }
    move = 0;
    //make a move to the best empty square
    while (move < board.size() && choice == -1)
    {
        if (isLegal(board, BEST_SQUARES[move]))
            choice = BEST_SQUARES[move];
        move++;
    }

    return choice;
}

void instructions()
{
    cout << "Welcome to the ultimate man-machine showdown: Tic-Tac-Toe.\n";
    cout << "--where human brain is pit against silicon processor\n\n";
    cout << "Make your move known by entering a number, 0 - 8. The number ";
    cout << "corresponds to the desired board position, as illustrated:\n";
    cout << "\t0 | 1 | 2\n";
    cout << "\t---------\n";
    cout << "\t3 | 4 | 5\n";
    cout << "\t---------\n";
    cout << "\t6 | 7 | 8\n\n";
    cout << "Prepare yourself, human. The battle is about to begin.\n\n";
}

void announceWinner(char winner, char& human, char& computer)
{
    char playAgain;
    if (winner == human)
        cout << "\nCongratulations! You won me.\n";
    else if (winner == computer)
        cout << "\nHaha, I won\n";
    else
        cout << "\nSo, that's tie.\n";
    cout << "\nDo you want to play yet? (y/n): ";
    cin >> playAgain;

    if (playAgain == 'y')
    {
        system("cls");
        main();
    }
    cout << "\nSee you next time!\n";
}

void displayBoard(const vector<char>& board)
{
    cout << "\n\t" << board[0] << " | " << board[1] << " | " << board[2] << "\n";
    cout << "\t---------\n";
    cout << "\t" << board[3] << " | " << board[4] << " | " << board[5] << "\n";
    cout << "\t---------\n";
    cout << "\t" << board[6] << " | " << board[7] << " | " << board[8] << "\n\n";
}

bool isLegal(const vector<char>& board, const int& move)
{
    if (board[move] == EMPTY)
        return true;
    else
        return false;
}

char detWinner(const vector<char>& board)
{
    const int WIN_POSITION[8][3] = {{0, 1 , 2}, {3, 4, 5}, {6, 7, 8}, {0, 3, 6}, {1, 4, 7}, {2, 5, 8}, {2, 4, 6}, {0, 4, 8}};

    for (int i = 0; i < 8; ++i)
    {
        if (board[WIN_POSITION[i][0]] == board[WIN_POSITION[i][1]]
            && board[WIN_POSITION[i][1]] == board[WIN_POSITION[i][2]]
            && board[WIN_POSITION[i][0]] != EMPTY)
        {
            return board[WIN_POSITION[i][0]];
        }

        if (count(board.begin(), board.end(), EMPTY) == 0)
            return TIE;
    }
    return NO_ONE;
}

char choice()
{
    char yesNo;
    cout << "\nDo you require the first move? (y/n): ";
    cin >> yesNo;

    if (yesNo == 'y')
        return X;
    else if (yesNo == 'n')
        return O;
    else
    {
        cout << "\nYou should enter only 'y' or 'n'\n";
        return choice();
    }
}