Develop Sudoku game using basic Windows Form and C# Dotnet codes

Hello friends, Let’s see how we can create a Sudoku puzzle game step by step using Windows Form and C# DotNet in Visual Studio without using any complex/advance codes neither external libraries.

Download the source code of the Sudoku Game

Prerequisites

• Basic c# programming knowledge
• Basic windows form application development knowledge
• Visual studio 2010+  

Step 1.

Start a new Windows Form Project in Visual Studio which will provide you the default form template and add a panel as shows in the below screenshot. 

Step 2.

Add new class for sudoku cells which by inheriting the button class.

  Copy Code Dude

using System.Windows.Forms;

namespace sudoku
{
    class SudokuCell : Button
    {
        public int Value { get; set; }
        public bool IsLocked { get; set; }
        public int X { get; set; }
        public int Y { get; set; }

        public void Clear()
        {
            this.Text = string.Empty;
            this.IsLocked = false;
        }
    }
}

Add Code in the code behind for the form in order to generate sudoku cells in the panel and click events for each cells (You can go to the code behind by right click on the form and select view code menu).

  Copy Code Dude

using System;
using System.Collections.Generic;
using System.Drawing;
using System.Linq;
using System.Windows.Forms;

namespace sudoku
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();

            createCells();
        }

        SudokuCell[,] cells = new SudokuCell[9, 9];

        private void createCells()
        {
            for (int i = 0; i < 9; i++)
            {
                for (int j = 0; j < 9; j++)
                {
                    // Create 81 cells for with styles and locations based on the index
                    cells[i, j] = new SudokuCell();
                    cells[i, j].Font = new Font(SystemFonts.DefaultFont.FontFamily, 20);
                    cells[i, j].Size = new Size(40, 40);
                    cells[i, j].ForeColor = SystemColors.ControlDarkDark;
                    cells[i, j].Location = new Point(i * 40, j * 40);
                    cells[i, j].BackColor = ((i / 3) + (j / 3)) % 2 == 0 ? SystemColors.Control : Color.LightGray;
                    cells[i, j].FlatStyle = FlatStyle.Flat;
                    cells[i, j].FlatAppearance.BorderColor = Color.Black;
                    cells[i, j].X = i;
                    cells[i, j].Y = j;

                    // Assign key press event for each cells
                    cells[i, j].KeyPress += cell_keyPressed;

                    panel1.Controls.Add(cells[i, j]);
                }
            }
        }

        private void cell_keyPressed(object sender, KeyPressEventArgs e)
        {
            var cell = sender as SudokuCell;

            // Do nothing if the cell is locked
            if (cell.IsLocked)
                return;

            int value;

            // Add the pressed key value in the cell only if it is a number
            if (int.TryParse(e.KeyChar.ToString(), out value))
            {
                // Clear the cell value if pressed key is zero
                if (value == 0)
                    cell.Clear();
                else
                    cell.Text = value.ToString();

                cell.ForeColor = SystemColors.ControlDarkDark;
            }
        }
    }
}

Let's run the application and see if the sudoku cells loads correctly 

Step 3.

Add code to load values in the cells. We have the logic to find valid numbers for each cell.

  Copy Code Dude

public Form1()
{
    InitializeComponent();

    createCells();

    startNewGame();
}

private void startNewGame()
{
    loadValues();
}

private void loadValues()
{
    // Clear the values in each cells
    foreach (var cell in cells)
    {
        cell.Value = 0;
        cell.Clear();
    }

    // This method will be called recursively 
    // until it finds suitable values for each cells
    findValueForNextCell(0, -1);
}

Random random = new Random();

private bool findValueForNextCell(int i, int j)
{
    // Increment the i and j values to move to the next cell
    // and if the columsn ends move to the next row
    if (++j > 8)
    {
        j = 0;

        // Exit if the line ends
        if (++i > 8)
            return true;
    }

    var value = 0;
    var numsLeft = new List<int> { 1, 2, 3, 4, 5, 6, 7, 8, 9 };

    // Find a random and valid number for the cell and go to the next cell 
    // and check if it can be allocated with another random and valid number
    do
    {
        // If there is not numbers left in the list to try next, 
        // return to the previous cell and allocate it with a different number
        if (numsLeft.Count < 1)
        {
            cells[i, j].Value = 0;
            return false;
        }

        // Take a random number from the numbers left in the list
        value = numsLeft[random.Next(0, numsLeft.Count)];
        cells[i, j].Value = value;

        // Remove the allocated value from the list
        numsLeft.Remove(value);
    }
    while (!isValidNumber(value, i, j) || !findValueForNextCell(i, j));

    // TDO: Remove this line after testing
    cells[i, j].Text = value.ToString();

    return true;
}

private bool isValidNumber(int value, int x, int y)
{
    for (int i = 0; i < 9; i++)
    {
        // Check all the cells in vertical direction
        if (i != y && cells[x, i].Value == value)
            return false;

        // Check all the cells in horizontal direction
        if (i != x && cells[i, y].Value == value)
            return false;
    }
            
    // Check all the cells in the specific block
    for (int i = x - (x % 3); i < x - (x % 3) + 3; i++)
    {
        for (int j = y - (y % 3); j < y - (y % 3) + 3; j++)
        {
            if (i != x && j != y && cells[i, j].Value == value)
                return false;
        }
    }

    return true;
}

We have the code to be removed as all the values won’t be shown to the player. It was included just to make sure the values are valid and proper while testing.

Let's run the application and see if the values loads correctly 

Now we can remove the code for showing the values in the cell.

Step 4.

Add code to show values in random based cells in order to work as hints

  Copy Code Dude

private void startNewGame()
{
    loadValues();

    //Show values of 45 cells as hint
    showRandomValuesHints(45);
}

Random random = new Random();

private void showRandomValuesHints(int hintsCount)
{
    // Show value in random cells
    // The hints count is based on the level player choose
    for (int i = 0; i < hintsCount; i++)
    {
        var rX = random.Next(9);
        var rY = random.Next(9);

        // Style the hint cells differently and
        // lock the cell so that player can't edit the value
        cells[rX, rY].Text = cells[rX, rY].Value.ToString();
        cells[rX, rY].ForeColor = Color.Black;
        cells[rX, rY].IsLocked = true;
    }
}

Let's run the application and see if the hints loads correctly 

As shown in the screenshot the hints are in black font colour and the user inputs are slightly light coloured (marked with red in the image).

Step 5.

Now let’s add the following controls in the form.

•  button for checking if the inputs are valid and if the player wins
• button for clearing all the inputs
• radio buttons for choosing the levels
• button for starting new game

·       

Now let’s add click events for the check input button which will do check if the game ends too.

  Copy Code Dude

private void checkButton_Click(object sender, EventArgs e)
{
    var wrongCells = new List<SudokuCell>();

    // Find all the wrong inputs
    foreach (var cell in cells)
    {
        if (!string.Equals(cell.Value.ToString(), cell.Text))
        {
            wrongCells.Add(cell);
        }
    }

    // Check if the inputs are wrong or the player wins 
    if (wrongCells.Any())
    {
        // Highlight the wrong inputs 
        wrongCells.ForEach(x => x.ForeColor = Color.Red);
        MessageBox.Show("Wrong inputs");
    }
    else
    {
        MessageBox.Show("You Wins");
    }
}

Add events for the clear and start new game button.

  Copy Code Dude

private void clearButton_Click(object sender, EventArgs e)
{
    foreach (var cell in cells)
    {
        // Clear the cell only if it is not locked
        if (cell.IsLocked == false)
            cell.Clear();
    }
}

private void newGameButton_Click(object sender, EventArgs e)
{
    startNewGame();
}

Modify the start game method to consider what level the player has chosen.

  Copy Code Dude

private void startNewGame()
{
    loadValues();

    var hintsCount = 0;

    // Assign the hints count based on the 
    // level player chosen
    if (beginnerLevel.Checked)
        hintsCount = 45;
    else if (IntermediateLevel.Checked)
        hintsCount = 30;
    else if (AdvancedLevel.Checked)
        hintsCount = 15;

    showRandomValuesHints(hintsCount);
}

Let’s run the application and see the check, clear and new game button works

Download the source code of the Sudoku Game

Enjoy Coding…!!!