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Random aZufallsgenerator = new Random();
aZufallsgenerator.Next(1, 200);

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PictureBox1.Visible = false;

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private void pictureBox1_Click(object sender, EventArgs e)
{
              aScore += 40;
              pictureBox1.Visible = false;
}

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

namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        const int geschwindigkeit = 30;
        const int refresh = 50;
        const int radius = 50;
        int x = 0, y = 0;
        Random r = new Random();

        private void timer1_Tick(object sender, EventArgs e)
        {
            int richtung = r.Next(360); //Winkel
            x += (int)(geschwindigkeit * Math.Sin(richtung));
            y += (int)(geschwindigkeit * Math.Cos(richtung));
            if (x < 0) x = 0;
            if (y < 0) y = 0;
            if (x > pictureBox1.Width - radius) x = pictureBox1.Width - radius;
            if (y > pictureBox1.Height - radius) y = pictureBox1.Height - radius;
            Graphics g = pictureBox1.CreateGraphics();
            //altes Bild löschen
            g.FillRectangle(new SolidBrush(Color.White), -1, -1, pictureBox1.Width + 1, pictureBox1.Height + 1);
            //neues Bild einfügen
            g.FillEllipse(new SolidBrush(Color.Red), x - radius, y - radius, 2 * radius, 2 * radius);
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            timer1.Enabled = true;
            timer1.Interval = refresh;
            x = r.Next(radius, pictureBox1.Width - radius);
            y = r.Next(radius, pictureBox1.Height - radius);
        }
    }
}

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PictureBox1.Visible = false;