16. Изчертаване на концентрични окръжности с различни цветове

   Bitmap bmp = new Bitmap(pictureBox1.Width, pictureBox1.Height); 
            Graphics graph = Graphics.FromImage(bmp); 
            Random r = new Random(); 
            int h = 100, red, green, blue; 
            for (int i=10; i<=320;i++) 
            { 
                int w=r.Next()%20 + 10; 
                red=r.Next()%256; 
                green=r.Next()%256; 
                blue=r.Next()%256; 
                Pen pen=new Pen(Color.FromArgb(red, green, blue),w); 
                graph.DrawEllipse(pen, 200-(i/2), 200-(i/2), i, i); 
                h=h+w/2;    
            } 
            pictureBox1.Image = bmp;