void Circle(int x, int y, int r,unsigned char color)
{
        int x1,y1,yk = 0;
        int sigma,delta,f;

        x1 = 0;
        y1 = r;
        delta = 2*(1-r);

        do
        {
                PutPixel(x+x1,y+y1,color);
                PutPixel(x-x1,y+y1,color);
                PutPixel(x+x1,y-y1,color);
                PutPixel(x-x1,y-y1,color);

                f = 0;
                if (y1 < yk)
                        break;
                if (delta < 0)
                {
                        sigma = 2*(delta+y1)-1;
                        if (sigma <= 0)
                        {
                                x1++;
                                delta += 2*x1+1;
                                f = 1;
                        }
                }
                else
                if (delta > 0)
                {
                        sigma = 2*(delta-x1)-1;
                        if (sigma > 0)
                        {
                                y1--;
                                delta += 1-2*y1;
                                f = 1;
                        }
                }
                if (!f)
                {
                        x1++;
                        y1--;
                        delta += 2*(x1-y1-1);
                }
        }
        while(1);
}