C#-Code

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace Minesweeper_Clone
{
    public partial class Form1 : Form
    {
        Spielfeld sf;
        public Form1()
        {
            InitializeComponent();
        }

        private void F_Click(object sender, EventArgs e)
        {
            Feld f = sender as Feld;
            if (f.IsBorder)
                return;

            if (f.IsBomb && (e as MouseEventArgs).Button == MouseButtons.Left && !f.IsFahne)
            {
                f.Clicked((e as MouseEventArgs).Button);
                MessageBox.Show("Verloren");
                return;
            }

            f.Clicked((e as MouseEventArgs).Button);

            if (Spielfeld.Completed)
                MessageBox.Show("Gewonnen");
        }

        private void btnStart_Click(object sender, EventArgs e)
        {
            sf = null;
            sf = new Spielfeld((int)nudSize.Value, (int)nudSize.Value, (int)nudBombs.Value);

            foreach (Feld f in sf.Gamepannel)
            {
                f.Click += F_Click;
                scPanel.Panel2.Controls.Add(f);
            }
            this.Invalidate();
        }
    }
}

C#-Code

using System;
using System.Collections.Generic;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace Minesweeper_Clone
{
    class Spielfeld
    {
        static Feld[,] gamepannel;
        static int openFields;
        static int felderCount;
        static int bombCount;
        static bool completed;

        public Feld[,] Gamepannel
        {
            get { return gamepannel; }
        }

        public static int OpenFields
        {
            get { return openFields; }
            set
            {
                openFields = value;
                if (openFields == felderCount - bombCount)
                    completed = true;
            }
        }

        public static bool Completed
        {
            get { return completed; }
        }
        public Spielfeld(int breite, int länge, int bombs)
        {
            bombCount = bombs;
            felderCount = breite * länge;
            openFields = 0;
            completed = false;
            gamepannel = new Feld[breite + 2, länge + 2];

            for (int i = 0; i < breite + 2; i++)
                gamepannel[0, i] = new Feld(0, i, true);
            for (int i = 0; i < länge + 2; i++)
                gamepannel[i, 0] = new Feld(i, 0, true);
            for (int i = 0; i < breite + 2; i++)
                gamepannel[breite + 1, i] = new Feld(breite + 1, i, true);
            for (int i = 0; i < länge + 2; i++)
                gamepannel[i, länge + 1] = new Feld(i, länge + 1, true);

            for (int i = 1; i <= breite; i++)
                for (int y = 1; y <= länge; y++)
                    gamepannel[i, y] = new Feld(i, y, false);

            for (int i = 0; i < bombCount; i++)
            {
                Random ran = new Random();
                int rx = ran.Next(1, breite + 1);
                int ry = ran.Next(1, länge + 1);

                if (gamepannel[rx, ry].IsBomb)
                {
                    i--;
                    continue;
                }

                gamepannel[rx, ry].IsBomb = true;
            }

            foreach (Feld f in gamepannel)
            {
                if (!f.IsBorder && !f.IsBomb)
                {
                    for (int i = f.X - 1; i <= f.X + 1; i++)
                        for (int y = f.Y - 1; y <= f.Y + 1; y++)
                            if (!gamepannel[i, y].IsBorder)
                                if (gamepannel[i, y].IsBomb)
                                    f.BombCount++;
                }
            }
        }
        public static void Freilegen(Feld f)
        {
            for (int i = f.X - 1; i <= f.X + 1; i++)
                for (int y = f.Y - 1; y <= f.Y + 1; y++)
                    if (!gamepannel[i, y].IsBorder)
                        gamepannel[i, y].Clicked(MouseButtons.Left);
        }
    }

    class Feld : PictureBox
    {
        const int rand = 30;
        const int feldgrösse = 30;
        bool isBomb;
        bool isBorder;
        bool isFahne;
        bool isOpened;
        int bombCount;
        int x;
        int y;

        public bool IsBomb
        {
            get { return isBomb; }
            set { isBomb = value; }
        }

        public bool IsBorder
        {
            get { return isBorder; }
            set
            {
                isBorder = value;
                if (value)
                    this.BackColor = Color.Black;
            }
        }

        public bool IsFahne
        {
            get { return isFahne; }
        }
        public int BombCount
        {
            get { return bombCount; }
            set { bombCount = value; }
        }

        public int X
        {
            get { return x; }
        }

        public int Y
        {
            get { return y; }
        }
        public Feld(int x, int y, bool boarder)
        {
            this.isOpened = false;
            this.isFahne = false;
            this.BackColor = Color.Gray;
            this.BackgroundImageLayout = ImageLayout.Stretch;
            this.x = x;
            this.y = y;
            this.Location = new Point(x * feldgrösse + rand, y * feldgrösse + rand);
            this.BorderStyle = BorderStyle.FixedSingle;
            this.Width = feldgrösse;
            this.Height = feldgrösse;
            this.IsBorder = boarder;
            this.IsBomb = false;
        }

        public void Clicked(MouseButtons b)
        {
            if (this.isOpened)
                return;

            if (b == MouseButtons.Left && !this.isFahne)
            {
                this.isOpened = true;
                Spielfeld.OpenFields++;

                if (isBomb)
                {
                    this.BackgroundImage = Image.FromFile(@"images/bomb.jpg");
                    return;
                }

                switch (bombCount)
                {
                    case 0:
                        this.BackColor = Color.White;
                         Spielfeld.Freilegen(this);
                        break;
                    case 1:
                        this.BackgroundImage = Image.FromFile(@"images/eins.jpg");
                        break;
                    case 2:
                        this.BackgroundImage = Image.FromFile(@"images/zwei.jpg");
                        break;
                    case 3:
                        this.BackgroundImage = Image.FromFile(@"images/drei.jpg");
                        break;
                    case 4:
                        this.BackgroundImage = Image.FromFile(@"images/vier.jpg");
                        break;
                    case 5:
                        this.BackgroundImage = Image.FromFile(@"images/fuenf.jpg");
                        break;
                    case 6:
                        this.BackgroundImage = Image.FromFile(@"images/sechs.jpg");
                        break;
                    case 7:
                        this.BackgroundImage = Image.FromFile(@"images/sieben.jpg");
                        break;
                    case 8:
                        this.BackgroundImage = Image.FromFile(@"images/acht.jpg");
                        break;
                    default:
                        break;
                }
            }

            if (b == MouseButtons.Right)
                if (!isFahne)
                {
                    this.isFahne = true;
                    this.BackgroundImage = Image.FromFile(@"images/fahne.png");
                }
                else
                {
                    this.isFahne = false;
                    this.BackgroundImage = null;
                    this.BackColor = Color.Gray;
                }
        }
    }
}