80 Answer ― Mandelbrot Set Function

int MandelSetCount( double startx, double starty, int limit)
{
  int count;
  double x=startx, y=starty;
  double newx, newy, funSq;
  funSq = startx*startx + starty*starty;
  
  for (count=0; count<limit &&  funSq<4.0; count++ )
  {
    newx = x*x - y*y + startx;
    newy = 2.0*x*y + starty;
    funSq = newx*newx + newy*newy;
    x = newx; y = newy;
  }
  return count ;
}

Comments: In this function, the value Ck is newx + j*newy; the value Ck2 is funSq.