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# Tic Tac Toe

This is an implementation of the Tic-tac-toe game.

We didn't put much effort in making a clever algorithm so it's not a challenge to play against the computer. Instead, study the source code to see how you can make reusable components such as the TicTacGameBoard widget.

Header file:

    /****************************************************************************
    ** $Id:  qt/tictac.h   3.0.0   edited Jun 22 13:24 $
    **
    ** Copyright (C) 1992-2000 Trolltech AS.  All rights reserved.
    **
    ** This file is part of an example program for Qt.  This example
    ** program may be used, distributed and modified without limitation.
    **
    *****************************************************************************/

    #ifndef TICTAC_H
    #define TICTAC_H

    #include <qpushbutton.h>
    #include <qptrvector.h>

    class QComboBox;
    class QLabel;

    // --------------------------------------------------------------------------
    // TicTacButton implements a single tic-tac-toe button
    //

    class TicTacButton : public QPushButton
    {
        Q_OBJECT
    public:
        TicTacButton( QWidget *parent );
        enum Type { Blank, Circle, Cross };
        Type        type() const            { return t; }
        void        setType( Type type )    { t = type; repaint(); }
        QSizePolicy sizePolicy() const
        { return QSizePolicy( QSizePolicy::Preferred, QSizePolicy::Preferred ); }
        QSize sizeHint() const { return QSize( 32, 32 ); }
        QSize minimumSizeHint() const { return QSize( 10, 10 ); }
    protected:
        void        drawButtonLabel( QPainter * );
    private:
        Type t;
    };

    // Using template vector to make vector-class of TicTacButton.
    // This vector is used by the TicTacGameBoard class defined below.

    typedef QPtrVector<TicTacButton>        TicTacButtons;
    typedef QMemArray<int>          TicTacArray;

    // --------------------------------------------------------------------------
    // TicTacGameBoard implements the tic-tac-toe game board.
    // TicTacGameBoard is a composite widget that contains N x N TicTacButtons.
    // N is specified in the constructor.
    //

    class TicTacGameBoard : public QWidget
    {
        Q_OBJECT
    public:
        TicTacGameBoard( int n, QWidget *parent=0, const char *name=0 );
       ~TicTacGameBoard();
        enum        State { Init, HumansTurn, HumanWon, ComputerWon, NobodyWon };
        State       state() const           { return st; }
        void        computerStarts( bool v );
        void        newGame();
    signals:
        void        finished();                     // game finished
    private slots:
        void        buttonClicked();
    private:
        void        setState( State state ) { st = state; }
        void        updateButtons();
        int checkBoard( TicTacArray * );
        void        computerMove();
        State       st;
        int         nBoard;
        bool        comp_starts;
        TicTacArray *btArray;
        TicTacButtons *buttons;
    };

    // --------------------------------------------------------------------------
    // TicTacToe implements the complete game.
    // TicTacToe is a composite widget that contains a TicTacGameBoard and
    // two push buttons for starting the game and quitting.
    //

    class TicTacToe : public QWidget
    {
        Q_OBJECT
    public:
        TicTacToe( int boardSize=3, QWidget *parent=0, const char *name=0 );
    private slots:
        void        newGameClicked();
        void        gameOver();
    private:
        void        newState();
        QComboBox   *whoStarts;
        QPushButton *newGame;
        QPushButton *quit;
        QLabel      *message;
        TicTacGameBoard *board;
    };

    #endif // TICTAC_H

Implementation:

    /****************************************************************************
    ** $Id:  qt/tictac.cpp   3.0.0   edited Jun 22 13:24 $
    **
    ** Copyright (C) 1992-2000 Trolltech AS.  All rights reserved.
    **
    ** This file is part of an example program for Qt.  This example
    ** program may be used, distributed and modified without limitation.
    **
    *****************************************************************************/

    #include "tictac.h"
    #include <qapplication.h>
    #include <qpainter.h>
    #include <qdrawutil.h>
    #include <qcombobox.h>
    #include <qcheckbox.h>
    #include <qlabel.h>
    #include <qlayout.h>
    #include <stdlib.h>                             // rand() function
    #include <qdatetime.h>                          // seed for rand()

    //***************************************************************************
    //* TicTacButton member functions
    //***************************************************************************

    // --------------------------------------------------------------------------
    // Creates a TicTacButton
    //

    TicTacButton::TicTacButton( QWidget *parent ) : QPushButton( parent )
    {
        t = Blank;                                  // initial type
    }

    // --------------------------------------------------------------------------
    // Paints TicTacButton
    //

    void TicTacButton::drawButtonLabel( QPainter *p )
    {
        QRect r = rect();
        p->setPen( QPen( white,2 ) );               // set fat pen
        if ( t == Circle ) {
            p->drawEllipse( r.left()+4, r.top()+4, r.width()-8, r.height()-8 );
        } else if ( t == Cross ) {                  // draw cross
            p->drawLine( r.topLeft()   +QPoint(4,4), r.bottomRight()-QPoint(4,4));
            p->drawLine( r.bottomLeft()+QPoint(4,-4),r.topRight()   -QPoint(4,-4));
        }
    }

    //***************************************************************************
    //* TicTacGameBoard member functions
    //***************************************************************************

    // --------------------------------------------------------------------------
    // Creates a game board with N x N buttons and connects the "clicked()"
    // signal of all buttons to the "buttonClicked()" slot.
    //

    TicTacGameBoard::TicTacGameBoard( int n, QWidget *parent, const char *name )
        : QWidget( parent, name )
    {
        st = Init;                                  // initial state
        nBoard = n;
        n *= n;                                     // make square
        comp_starts = FALSE;                        // human starts
        buttons = new TicTacButtons(n);             // create real buttons
        btArray = new TicTacArray(n);               // create button model
        QGridLayout * grid = new QGridLayout( this, 3, 3, 4 );
        QPalette p( blue );
        for ( int i=0; i<n; i++ ) {                 // create and connect buttons
            TicTacButton *ttb = new TicTacButton( this );
            ttb->setPalette( p );
            ttb->setEnabled( FALSE );
            connect( ttb, SIGNAL(clicked()), SLOT(buttonClicked()) );
            grid->addWidget( ttb, i%3, i/3 );
            buttons->insert( i, ttb );
            btArray->at(i) = TicTacButton::Blank;   // initial button type
        }
        QTime t = QTime::currentTime();             // set random seed
        srand( t.hour()*12+t.minute()*60+t.second()*60 );
    }

    TicTacGameBoard::~TicTacGameBoard()
    {
        delete buttons;
        delete btArray;
    }

    // --------------------------------------------------------------------------
    // TicTacGameBoard::computerStarts( bool v )
    //
    // Computer starts if v=TRUE. The human starts by default.
    //

    void TicTacGameBoard::computerStarts( bool v )
    {
        comp_starts = v;
    }

    // --------------------------------------------------------------------------
    // TicTacGameBoard::newGame()
    //
    // Clears the game board and prepares for a new game
    //

    void TicTacGameBoard::newGame()
    {
        st = HumansTurn;
        for ( int i=0; i<nBoard*nBoard; i++ )
            btArray->at(i) = TicTacButton::Blank;
        if ( comp_starts )
            computerMove();
        else
            updateButtons();
    }

    // --------------------------------------------------------------------------
    // TicTacGameBoard::buttonClicked()             - SLOT
    //
    // This slot is activated when a TicTacButton emits the signal "clicked()",
    // i.e. the user has clicked on a TicTacButton.
    //

    void TicTacGameBoard::buttonClicked()
    {
        if ( st != HumansTurn )                     // not ready
            return;
        int i = buttons->findRef( (TicTacButton*)sender() );
        TicTacButton *b = buttons->at(i);           // get piece that was pressed
        if ( b->type() == TicTacButton::Blank ) {   // empty piece?
            btArray->at(i) = TicTacButton::Circle;
            updateButtons();
            if ( checkBoard( btArray ) == 0 )       // not a winning move?
                computerMove();
            int s = checkBoard( btArray );
            if ( s ) {                              // any winners yet?
                st = s == TicTacButton::Circle ? HumanWon : ComputerWon;
                emit finished();
            }
        }
    }

    // --------------------------------------------------------------------------
    // TicTacGameBoard::updateButtons()
    //
    // Updates all buttons that have changed state
    //

    void TicTacGameBoard::updateButtons()
    {
        for ( int i=0; i<nBoard*nBoard; i++ ) {
            if ( buttons->at(i)->type() != btArray->at(i) )
                buttons->at(i)->setType( (TicTacButton::Type)btArray->at(i) );
            buttons->at(i)->setEnabled( buttons->at(i)->type() ==
                                        TicTacButton::Blank );
        }
    }

    // --------------------------------------------------------------------------
    // TicTacGameBoard::checkBoard()
    //
    // Checks if one of the players won the game, works for any board size.
    //
    // Returns:
    //  - TicTacButton::Cross  if the player with X buttons won
    //  - TicTacButton::Circle if the player with O buttons won
    //  - Zero (0) if there is no winner yet
    //

    int TicTacGameBoard::checkBoard( TicTacArray *a )
    {
        int  t = 0;
        int  row, col;
        bool won = FALSE;
        for ( row=0; row<nBoard && !won; row++ ) {  // check horizontal
            t = a->at(row*nBoard);
            if ( t == TicTacButton::Blank )
                continue;
            col = 1;
            while ( col<nBoard && a->at(row*nBoard+col) == t )
                col++;
            if ( col == nBoard )
                won = TRUE;
        }
        for ( col=0; col<nBoard && !won; col++ ) {  // check vertical
            t = a->at(col);
            if ( t == TicTacButton::Blank )
                continue;
            row = 1;
            while ( row<nBoard && a->at(row*nBoard+col) == t )
                row++;
            if ( row == nBoard )
                won = TRUE;
        }
        if ( !won ) {                               // check diagonal top left
            t = a->at(0);                           //   to bottom right
            if ( t != TicTacButton::Blank ) {
                int i = 1;
                while ( i<nBoard && a->at(i*nBoard+i) == t )
                    i++;
                if ( i == nBoard )
                    won = TRUE;
            }
        }
        if ( !won ) {                               // check diagonal bottom left
            int j = nBoard-1;                       //   to top right
            int i = 0;
            t = a->at(i+j*nBoard);
            if ( t != TicTacButton::Blank ) {
                i++; j--;
                while ( i<nBoard && a->at(i+j*nBoard) == t ) {
                    i++; j--;
                }
                if ( i == nBoard )
                    won = TRUE;
            }
        }
        if ( !won )                                 // no winner
            t = 0;
        return t;
    }

    // --------------------------------------------------------------------------
    // TicTacGameBoard::computerMove()
    //
    // Puts a piece on the game board. Very, very simple.
    //

    void TicTacGameBoard::computerMove()
    {
        int numButtons = nBoard*nBoard;
        int *altv = new int[numButtons];            // buttons alternatives
        int altc = 0;
        int stopHuman = -1;
        TicTacArray a = btArray->copy();
        int i;
        for ( i=0; i<numButtons; i++ ) {            // try all positions
            if ( a[i] != TicTacButton::Blank )      // already a piece there
                continue;
            a[i] = TicTacButton::Cross;             // test if computer wins
            if ( checkBoard(&a) == a[i] ) {         // computer will win
                st = ComputerWon;
                stopHuman = -1;
                break;
            }
            a[i] = TicTacButton::Circle;            // test if human wins
            if ( checkBoard(&a) == a[i] ) {         // oops...
                stopHuman = i;                      // remember position
                a[i] = TicTacButton::Blank;         // restore button
                continue;                           // computer still might win
            }
            a[i] = TicTacButton::Blank;             // restore button
            altv[altc++] = i;                       // remember alternative
        }
        if ( stopHuman >= 0 )                       // must stop human from winning
            a[stopHuman] = TicTacButton::Cross;
        else if ( i == numButtons ) {               // tried all alternatives
            if ( altc > 0 )                         // set random piece
                a[altv[rand()%(altc--)]] = TicTacButton::Cross;
            if ( altc == 0 ) {                      // no more blanks
                st = NobodyWon;
                emit finished();
            }
        }
        *btArray = a;                               // update model
        updateButtons();                            // update buttons
        delete[] altv;
    }

    //***************************************************************************
    //* TicTacToe member functions
    //***************************************************************************

    // --------------------------------------------------------------------------
    // Creates a game widget with a game board and two push buttons, and connects
    // signals of child widgets to slots.
    //

    TicTacToe::TicTacToe( int boardSize, QWidget *parent, const char *name )
        : QWidget( parent, name )
    {
        QVBoxLayout * l = new QVBoxLayout( this, 6 );

        // Create a message label

        message = new QLabel( this );
        message->setFrameStyle( QFrame::WinPanel | QFrame::Sunken );
        message->setAlignment( AlignCenter );
        l->addWidget( message );

        // Create the game board and connect the signal finished() to this
        // gameOver() slot

        board = new TicTacGameBoard( boardSize, this );
        connect( board, SIGNAL(finished()), SLOT(gameOver()) );
        l->addWidget( board );

        // Create a horizontal frame line

        QFrame *line = new QFrame( this );
        line->setFrameStyle( QFrame::HLine | QFrame::Sunken );
        l->addWidget( line );

        // Create the combo box for deciding who should start, and
        // connect its clicked() signals to the buttonClicked() slot

        whoStarts = new QComboBox( this );
        whoStarts->insertItem( "Computer starts" );
        whoStarts->insertItem( "Human starts" );
        l->addWidget( whoStarts );

        // Create the push buttons and connect their clicked() signals
        // to this right slots.

        newGame = new QPushButton( "Play!", this );
        connect( newGame, SIGNAL(clicked()), SLOT(newGameClicked()) );
        quit = new QPushButton( "Quit", this );
        connect( quit, SIGNAL(clicked()), qApp, SLOT(quit()) );
        QHBoxLayout * b = new QHBoxLayout;
        l->addLayout( b );
        b->addWidget( newGame );
        b->addWidget( quit );

        newState();
    }

    // --------------------------------------------------------------------------
    // TicTacToe::newGameClicked()                  - SLOT
    //
    // This slot is activated when the new game button is clicked.
    //

    void TicTacToe::newGameClicked()
    {
        board->computerStarts( whoStarts->currentItem() == 0 );
        board->newGame();
        newState();
    }

    // --------------------------------------------------------------------------
    // TicTacToe::gameOver()                        - SLOT
    //
    // This slot is activated when the TicTacGameBoard emits the signal
    // "finished()", i.e. when a player has won or when it is a draw.
    //

    void TicTacToe::gameOver()
    {
        newState();                                 // update text box
    }

    // --------------------------------------------------------------------------
    // Updates the message to reflect a new state.
    //

    void TicTacToe::newState()
    {
        static const char *msg[] = {                // TicTacGameBoard::State texts
            "Click Play to start", "Make your move",
            "You won!", "Computer won!", "It's a draw" };
        message->setText( msg[board->state()] );
        return;
    }

Main:

    /****************************************************************************
    ** $Id:  qt/main.cpp   3.0.0   edited Jun 22 13:24 $
    **
    ** Copyright (C) 1992-2000 Trolltech AS.  All rights reserved.
    **
    ** This file is part of an example program for Qt.  This example
    ** program may be used, distributed and modified without limitation.
    **
    *****************************************************************************/

    #include <qapplication.h>
    #include <stdlib.h>
    #include "tictac.h"

    int main( int argc, char **argv )
    {
        QApplication a( argc, argv );
        int n = 3;
        if ( argc == 2 )                            // get board size n
            n = atoi(argv[1]);
        if ( n < 3 || n > 10 ) {                    // out of range
            qWarning( "%s: Board size must be from 3x3 to 10x10", argv[0] );
            return 1;
        }
        TicTacToe ttt( n );                         // create game
        a.setMainWidget( &ttt );
        ttt.setCaption("Qt Example - TicTac");
        ttt.show();                                 // show widget
        return a.exec();                            // go
    }

See also Examples.