OPTION SHOW OFF
OPTION ESCAPE OFF

dim r as double

sub draw_circle
  dim x0 as int
  dim y0 as int
  dim x1 as int
  dim y1 as int
  dim angle as double
  dim start as double
  dim stp as double
  dim inc as double
  dim theta as double
  cls

'  printxy -70,-40,r

  start = 0
  stp = 6.28
  inc = 0.628
  theta = 0.0628*r
  angle = 0
  x0=sin(angle+theta)*r
  y0=cos(angle+theta)*r
  while (angle < stp)
    x1=sin(angle+theta)*r
    y1=cos(angle+theta)*r
    line x0, y0, x1, y1
    x0=x1
    y0=y1
    angle = angle + inc
  wend
  angle=theta
  x1=sin(angle)*r
  y1=cos(angle)*r
  line x0, y0, x1, y1


  REDRAW SHOW

end sub

r = 10

draw_circle

while true
'  inline _escape(0);

  if key(#KEY_LEFT) then
    r=r+1
    draw_circle(r)
  endif
  if key(#KEY_RIGHT) then
    r=r-1
    draw_circle(r)
  endif
  if key(#KEY_SPACE) then exit while
wend