编写一个模拟龟兔赛跑的窗体应用程序，绘制不同颜色的两个圆分别代表乌龟和兔子，设置一个按钮，单击按键后，龟兔开始赛跑。

以下是一个简单的模拟龟兔赛跑的窗体应用程序，使用 C# 语言和 Windows Forms 库绘制不同颜色的两个圆分别代表乌龟和兔子，并设置一个按钮，单击按键后，龟兔开始赛跑：

using System;
using System.Drawing;
using System.Windows.Forms;

namespace TurtleAndRabbitRace
{
    public partial class Form1 : Form
    {
        private const int RACE_TRACK_LENGTH = 500;
        private const int RACE_TRACK_WIDTH = 100;
        private const int TURTLE_START_POS = 0;
        private const int RABBIT_START_POS = 0;
        private const int TURTLE_SPEED = 10;
        private const int RABBIT_SPEED = 20;
        private const int FINISH_LINE = RACE_TRACK_LENGTH - RACE_TRACK_WIDTH;

        private readonly Random random = new Random();
        private int turtlePos = TURTLE_START_POS;
        private int rabbitPos = RABBIT_START_POS;

        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Paint(object sender, PaintEventArgs e)
        {
            Graphics graphics = e.Graphics;

            // Draw the race track
            Pen pen = new Pen(Color.Black, RACE_TRACK_WIDTH);
            graphics.DrawLine(pen, 0, ClientSize.Height / 2, ClientSize.Width, ClientSize.Height / 2);

            // Draw the turtle and rabbit
            Brush turtleBrush = new SolidBrush(Color.Green);
            Brush rabbitBrush = new SolidBrush(Color.Red);
            graphics.FillEllipse(turtleBrush, turtlePos, ClientSize.Height / 2 - RACE_TRACK_WIDTH / 2, RACE_TRACK_WIDTH, RACE_TRACK_WIDTH);
            graphics.FillEllipse(rabbitBrush, rabbitPos, ClientSize.Height / 2 - RACE_TRACK_WIDTH / 2 - RACE_TRACK_WIDTH, RACE_TRACK_WIDTH, RACE_TRACK_WIDTH);
        }

        private void button1_Click(object sender, EventArgs e)
        {
            timer1.Start();
        }

        private void timer1_Tick(object sender, EventArgs e)
        {
            // Move the turtle and rabbit randomly
            turtlePos += TURTLE_SPEED;
            rabbitPos += RABBIT_SPEED * random.Next(2);

            // Check if they have reached the finish line
            if (turtlePos >= FINISH_LINE || rabbitPos >= FINISH_LINE)
            {
                timer1.Stop();

                if (turtlePos > rabbitPos)
                {
                    MessageBox.Show("Turtle wins!");
                }
                else if (rabbitPos > turtlePos)
                {
                    MessageBox.Show("Rabbit wins!");
                }
                else
                {
                    MessageBox.Show("It's a tie!");
                }

                // Reset the positions
                turtlePos = TURTLE_START_POS;
                rabbitPos = RABBIT_START_POS;
            }

            Invalidate();
        }
    }
}

在窗体上添加一个按钮和一个 Timer 控件，并将 Timer 控件的 Interval 属性设置为 100，然后将上述代码复制到窗体类中即可。

当单击按钮时，程序将启动 Timer 控件，并每 100 毫秒重绘窗体以更新乌龟和兔子的位置。每次 Tick 事件发生时，程序将随机移动乌龟和兔子，并检查它们是否已经到达终点线。如果是，则停止计时器，并显示获胜者。最后，程序将重置乌龟和兔子的位置，以便下一次比赛。