C++ was used to make this application. Qt framework was used to make GUI.

Sudoku puzzle game with numbers was created in the course of the work. The internal structure of application is described in app/grid directory. The appearance is described in app/windows directory.

The application consists of main menu and game window.

To set the "grid" and interact with it, a Grid class has been created with two fields matrix and solving - solved and unsolved matrices, respectively. To create matrices, the QVector class from the Qt framework is used.

In the constructor of the Grid class, the matrix field is formed by setting the "base" matrix according to the previously described algorithm. Legal transformations are transposition - the transpose() method, the exchange of two rows within the same area - the swapRows() method and the exchange of two columns within the same area - the swapColumns() method. Using the mix() method, the elements of the matrix are "mixed": one of the three matrix transformation methods is randomly called 18 times. Thus, a high speed of operation and sufficient randomness of the "grid" is achieved.

Using the resetToZero() method, an unsolved matrix is formed: the matrix is copied to solving and elements of the "grid" are randomly selected, which are then "deleted", that is, these elements take a zero value. The number of selected cells depends on the selected difficulty level, which is passed as a parameter to the method. Thus, 51, 31 or 21 filled cells may remain.

The main menu is created using the MainMenu class, which is inherited from QWidget. It has a fixed size of 500 by 500 pixels. The background is a .png image located in the background_label object of the QLabel type using the predefined setPixmap() method. In the main menu there are 3 buttons of the QPushButton type (start_button, about_button, quit_button) grouped using the main_box object of the QGroupBox type. The style of the buttons is set using the predefined setStyleSheet() method, the kButtonStyle string of the QString type is passed to it as a parameter. The main_box box style is set by the same method using a cboxstyle string of type QString. kButton Style and kBoxStyle are constant members of the MainMenu class.

• The "Start game" (start_button) button opens the game window using the QObject::connect binding(start_button, SIGNAL(clicked()), this, SLOT(gameWindowOpen())), where gameWindowOpen() is a slot that implements switching to the game window.

• Button "More about the game" (about_button) opens an additional window on top of the main one, using the binding QObject::connect(about_button, SIGNAL(clicked()), this, SLOT(aboutWindowOpen())), where aboutWindowOpen() is a slot that implements the creation of an additional window about_window. The additional window is an object of the AboutWindow class. This class inherits from the QDialog. about_window class contains the name of the game and the name of the developer, while it is open, there is no way to interact with the main window.

• The "Exit" button closes the main window and thereby terminates the program using QObject::connect(quit_button, SIGNAL(clicked()), this, SLOT(close())), where close() is a predefined slot.

The game window is described by the GameWindow class, which inherits from QWidget. The window has a fixed size of 680 by 710 pixels. In the game window there are 4 buttons of the QPushButton type (return_button, generate_button, check_button, solve_button), a button with a pop-up list of the QComboBox type (diff_box), "grid" - a two-dimensional vector of the QVector type of fields for entering the QLineEdit type (grid), as well as a field type Area. The Area class is inherited from QLabel and the paintEvent() event is redefined in it. In the paintEvent() method, a QPainter type object is created and using the drawLine() method, lines are drawn - the boundaries of the regions-sections on the Sudoku grid. The styles of all objects located in the widget of the game window are set by the setStyleSheet() method and constant strings kButtonStyle and kBoxStyle of the QString type.

• The "Return" button (return_button) returns the user to the main menu using QObject::connect(return_button, SIGNAL(clicked()), this, SLOT(returnButtonClicked())), where returnButtonClicked() is the slot that closes the game window and opens the main menu window.

• The Generate (generate_button) button fills the grid with numbers using the QObject::connect binding(generate_button, SIGNAL(clicked()), this, SLOT(generateGrid())). When calling the generateGrid() slot, the current difficulty level is taken from the diff_box list, the constructor of the Grid class is called, that is, the Grid::matrix matrix is filled with numbers, and then the resetToZero() method of the Grid class is called, the value of the difficulty level is passed to its parameters. Then the "grid" of the game window is filled in accordance with the values of the Grid::solving matrix, partially filled with zeros. Zeros are not output at the same time, and instead of them there are empty editable text input fields that differ in color. Filled cells are not editable.

• The button with a pop-up list (diff_box) allows you to choose one of three difficulty levels: easy, medium, hard.

• Button "Check" (check_button) checks the user-filled cells "grids" using the binding QObject::connect(check_button, SIGNAL(clicked()), this, SLOT(checkSol())). When calling the checkSol() slot, the values of the grid, which are editable, are compared step by step with the corresponding values of the Grid::matrix matrix. If an incorrect value is written in a particular cell, then the field acquires a red outline. If all the values match, an additional window of the AboutWindow type opens with a notification of the correct decision.

• The button "Solve" (solve_button) outputs a correctly solved Sudoku using the binding QObject::connect(resolve_button, SIGNAL(clicked()), this, SLOT(solveGenerated())). When the solveGenerated() slot is called, the values of the Grid::matrix matrix are assigned to the values of the grid element by element. In this case, all fields become non-editable.

Also, the closeEvent() event has been redefined in the GameWindow class. When the game window is closed, this event is called, which opens the main menu window.

Additional methods setQLEStyle(), setQLEStyleEditable(), setQLEStyleMistake(), setButtonStyle() and CellEdit() are needed to change the appearance of buttons and text fields.