What's wrong with my code? Tic Tac Toe

[DELB]

//

 Tic Tac Toe.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"
#include <iostream>
#include <string>
#include <vector>
#include <algorithm>

using namespace std;

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

// function prototypes
void instructions();
char askYesNo(string question);
int askNumber(string question, int high, int low = 0);
char humanPiece();
char opponent(char piece);
void displayBoard(const vector<char>& board);
char winner(const vector<char>& board);
bool isLegal(const vector<char>& board, char human);
int computerMove(vector<char> board, char computer);
void announceWinner(char winner, char computer, char human);

// main function

int _tmain(int argc, _TCHAR* argv[])
{
	int move;
	const int NUM_SQUARES = 9;
	vector<char> board(NUM_SQUARES, EMPTY);

	instructions();
	char human = humanPiece();
	char computer = opponent(human);
	char turn = X;
	displayBoard(board);

	while (winner(board) == NO_ONE)
	{
		if (turn == human)
		{
			move = humanMove(board, human);
			board[move] = human;
		}
		else
		{
			move = computerMove(board, computer);
			board[move] = computer;
		}
		displayBoard(board);
		turn = opponent(turn);
	}

	announceWinner(winner(board), computer, human);

	return 0;
}

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\n";
	cout << "corresponds to the desired board position, as illustrated:\n\n";

	cout << "		0 | 1 | 2\n";
	cout << "		-----\n";
	cout << "		3 | 4 | 5\n";
	cout << "		-----\n";
	cout << "		6 | 7 | 8\n\n";

	cout << "Prepare yourself, human.  The battle is about to begin.\n\n";
}

char askYesNo(string question)
{
	char response;
	do
	{
		cout << question << " (y/n): ";
		cin >> response;
	}
	while (response != 'y' && response != 'n');

	return response;
}

int askNumber(string question, int high, int low)
{
	int number;
	do
	{
		cout << question << " (" << low << " - " << high << "): ";
		cin >> number;
	}
	while (number > high || number < low);

	return number;
}

char humanPiece()
{
	char go_first = askYesNo("Do you require the first move?");
	if (go_first == 'y')
	{
		cout << "\nThen take the first move.  You will need it\n";
		return X;
	}
	else
	{
		cout << "\nYour bravery will be your undoing...  I will go first.\n";
		return 0;
	}
}

char opponent(char piece)
{
	if (piece == X)
		return O;
	else
		return X;
}

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

char winner(const vector<char>& board)
{
	// all possible winning rows
	const int WINNING_ROWS[8][3] = { {0, 1, 2},
										{3, 4, 5},
										{6, 7, 8},
										{0, 3, 6},
										{1, 4, 7},
										{2, 5, 8},
										{0, 4, 8},
										{2, 4, 6} };
	const int TOTAL_ROWS = 8;

	// if any winning row as three values that are the same (and NOT EMPTY),
	// then we have a winner
	for(int row = 0; row < TOTAL_ROWS; ++row)
	{
		if ( (board[WINNING_ROWS[row][0]] != EMPTY) &&
			 (board[WINNING_ROWS[row][0]] == board[WINNING_ROWS[row][1]]) &&
			 (board[WINNING_ROWS[row][1]] == board[WINNING_ROWS[row][2]) )
		{
			return board[WINNING_ROWS[row][0]];
		}

	// since nobody has won, check for a tie (no empty squares left)
	if (count(board.begin(), board.end(), EMPTY) == 0)
		return TIE;

	// since nobody has won and it isn't a tie, the game ain't over
	return NO_ONE;
}

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

int humanMove(const vector<char>& board, char human)
{
	int move = askNumber("Where will you move?", (board.size() - 1));
	while (!isLegal(move, board))
	{
		cout << "\nThat sqaure is already occupied, foolish human.\n";
		move = askNumber("Where will you move?", (board.size() - 1));
	}
	cout << "Fine...\n";
	return move;
}

int computerMove(vector<char> board, char computer)
{
	cout << "I shall take square number ";

	// if computer can win on next move, make that move
	for(int move = 0; move < board.size(); ++move)
	{
		if (isLegal(move, board))
		{
			board[move] = computer;
			if (winner(board) == computer)
			{
				cout << move << endl;
				return move;
			}
			// done checking this move, undo it
			board[move] = EMPTY;
		}
	}

	// if human can win on next move, block that move
	char human = opponent(computer);
	for(int move = 0; move < board.size(); ++move)
	{
		if (isLegal(move, board))
		{
			board[move] = human;
			if (winner(board) == human)
			{
				cout << move << endl;
				return move;
			}
			// done checking this move, undo it
			board[move] = EMPTY;
		}
	}

	// the bestmoves to make, in order
	const int BEST_MOVES[] = {4, 0, 2, 6, 8, 1, 3, 5, 7};
	// since no one can win on next move, pick best open square
	for(int i = 0; i < board.size(); ++i)
	{
		int move = BEST_MOVES[i];
		if (isLegal(move, board))
		{
			cout << move << endl;
			return move;
		}
	}
}

void announceWinner(char winner, char computer, char human)
{
	if (winner == computer)
	{
		cout << winner << "'s won!\n";
		cout << "As I predicted, human, I am trimphunt once more -- proof\n";
		cout << "that computers are superior to humans in all regards.\n";
	}
	else if (winner == human)
	{
		cout << winner << "'s won!\n";
		cout << "No, no!  It cannot be!  Somehow you tricked me, human.\n";
		cout << "But never gain!  I, the computer, so swear it!\n";
	}
	else
	{
		cout << "It's a tie.\n";
		cout << "You were most lucky, human, and somehow manage to tie me.\n";
		cout << "Celebrate...  for this is the best you will ever achieve.\n";
	}
}

Can anyone find anything wrong with it? I've checked through it several times and it just won't compile :(.

[Lynx876]

From a quick read through. You have no function prototype of:
int humanMove(const vector<char>& board, char human);

Line 134:
cout << "\n\t" << board[0] " | " << board[1] << " | " << board[2];

Should be:
cout << "\n\t" << board[0] << " | " << board[1] << " | " << board[2];

Line 161:
(board[WINNING_ROWS[row][1]] == board[WINNING_ROWS[row][2]) )

Should be:
(board[WINNING_ROWS[row][1]] == board[WINNING_ROWS[row][2]]) )

The for-loop on line 157 is missing a matching brace } on line 165.

[DELB]

Thanks man, it works. I keep seeing those instances of [move] all of the time, but I have no idea what they do. Could you or someone please explain to me what it does? Thank you.

Another query as well:
void displayBoard(const vector<char>& board)

{
	cout << "\n\t" << board[0] " | " << board[1] << " | " << board[2];
	cout << "\n\t" << "----";
	cout << "\n\t" << board[3] << " | " << board[4] << " | " << board[5];
	cout << "\n\t" << "----";
	cout << "\n\t" << board[6] << " | " << board[7] << " | " << board[8];
	cout << "\n\t";
}

How does the board's in there get the noughts and crosses?

[Lynx876]

No problem. But I'm guessing this isn't your code?!

And the board from the above code, is populated by the vector, board[ 0 ] etc.

[DELB]

Heh, nah this isn't my code. It's Michael Dawson's code from the "Beginners Guide to C++ Game Programming". Been programming with C++ for about 3 months now though so I'm getting the hang of understanding things, just buying loads of books and getting the hang of it.

What about [move]? :).

Oh and:
move = askNumber("Where will you move?", (board.size() - 1));

(board.size() - 1));

What does the -1 do in this?

[Lynx876]

board[move] is accessing the board, with the index of move.

move being an index number.

And from a quick read through. I'm guessing that board.size() - 1 is so that you don't 'run off' you allocated memory.

When you declare an array etc. myArray[ 5 ];, you use the array as n-1

This is because an array starts from 0. So 0 - 4 would be 5 indices! (n-1), n being the number for the array creation.

[DELB]

Thank you!

[DELB]

Right one more question:

		if ( (board[WINNING_ROWS[row][0]] != EMPTY) &&
			 (board[WINNING_ROWS[row][0]] == board[WINNING_ROWS[row][1]]) &&
			 (board[WINNING_ROWS[row][1]] == board[WINNING_ROWS[row][2]) )
		{
			return board[WINNING_ROWS[row][0]];
		}

See that
return board[WINNING_ROWS[row][0]];

Is that basically else?

[Lynx876]

No.

The if statement checks to see if the board is empty. If it's not, it checks to see if all 3 indices are the same. If they are the same, it will return a character of the winning symbol. 'X' or 'O'.

return = exit the current function and return a char.

This is used to exit the while loop on line 45. Which will end the game.

[DELB]

I don't suppose you could narrow it down a bit more? :-).

[Lynx876]

I think that's about as narrow as it gets... lol.

uhm. returning something from a function is the same as assignment.

i.e.
char winningChar = winner( board );

What ever is returned from the function winner( board ) will be saved in the variable winningChar

[DELB]

I think the thing I'm getting confused at is what exactly is returned from return board[WINNING_ROWS[row][0]]; and when does it actually happen.

[Lynx876]

It only returns at that point if there's a winning line.

Winning lines are these combinations:

const int WINNING_ROWS[8][3] = { {0, 1, 2},
				{3, 4, 5},
				{6, 7, 8},
				{0, 3, 6},
				{1, 4, 7},
				{2, 5, 8},
				{0, 4, 8},
				{2, 4, 6} };

if ( (board[WINNING_ROWS[row][0]] != EMPTY) ...
So, if it's not empty, a space( ' ' ), then it has to be either an 'X' or 'O'.

So, lets take this winning line:
{0, 1, 2}

Say 0, 1 and 2 contain an 'X'.

(board[WINNING_ROWS[row][0]] == board[WINNING_ROWS[row][1]]) &&
(board[WINNING_ROWS[row][1]] == board[WINNING_ROWS[row][2]) )

If 0 is not empty, which it's not, it has an 'X' in.
AND 0 is the same as 1,
AND 1 is the same as 2 ( Meaning, 0, 1 and 2 contain the same! )
THEN, return 'X', which is the contents of 0( return board[WINNING_ROWS[row][0]]; )

[DELB]

Okay so when you say it returns 'X' it returns X to the screen? Also the [0] [1] [2] is what? Is it 0, 1, 2 in the winning rows?

I get all of the rest of the program but not this.

[Lynx876]

Line 61:
announceWinner(winner(board), computer, human);

A call to announce the winner.


The announceWinner function:
void announceWinner(char winner, char computer, char human)

This function takes: char, char, char

So, the return of winner( board ) will be sent to the announceWinner function as the first parameter. Which is the returned char.

Also the [0] [1] [2] is what? Is it 0, 1, 2 in the winning rows?

Yes.

[DELB]

Brilliant. Thank you.

[Lynx876]

No problem! Glad you understand it! (: