'Mandelbrot Set Generator in QuickBASIC
'by Robert John Morton

'TO GENERATE THE MANDLEBROT SET [Compiled as mandel.exe]

screen 9, 3 : locate 1,1
xbias = 400 : ybias = 200
   cy = -1.5
A: cx = -2.5
B: x = .01 : y = .01 : i = 0
L: if inkey$ > "" then 
     locate 24,1: print"Terminated by User";:end
   end if
   z = x * y                  'square x + iy and add cx + icy
   x = x * x - y * y + cx
   y = z + z + cy 
   for j = 1 to 50 : next     'delay re GCA display problem
   if x < -2 or x > +2 or y < -2 or y > +2 goto Q   'diverged
   if i < 500 then i = i + 1 : goto L
M: if cx < 1 then cx = cx + .01 : goto B
   if cy < 1.5 then cy = cy + .01 : goto A
   end

Q: if i < 10 then
      c = 9                            'blue
   elseif i < 20 then
      c = 10                           'green
   elseif i < 40 then
      c = 11                           'cyan
   elseif i < 80 then
      c = 12                           'red
   elseif i < 160 then
      c = 13                           'purple
   else
      c = 14                           'yellow
   end if
P: pset(xbias + cx * 150, ybias - cy * 100), c : goto M

# 1997 Robert John Morton