dim plane(100,100)
x  = 50: y = 50: minY = 100

while (x>0) and (x<100) and (y>0) and (y<100)
 if plane(x,y) then
   nxt = nxt - 1
   if nxt < 1 then nxt = 4
  else
   nxt = nxt + 1
   if nxt > 4 then nxt = 1
 end if

 x          = x + (nxt = 2) - (nxt = 4)
 y          = y + (nxt = 3) - (nxt = 1)
 plane(x,y) = (plane(x,y) <> 1)
 minY       = min(y,minY)          ' find lowest and
 maxY       = max(y,maxY)          '  highest y to prevent printing blank lines
wend

graphic #g, 100,100
for y = minY to maxY
  for x = 1 to 100
   print chr$((plane(x,y)*3) + 32);
     if plane(x,y) = 1 then  #g "color green ; set "; x; " "; y else #g "color blue ; set "; x; " "; y
  next x
  print y
next y
render #g
#g "flush""