On Thu, 5 Nov 1998, Sean Breheny wrote:

> Hi Scott,
>
> I just went to that link and directly converted Andy's pseudocode into
> BASIC code and it produces a diamond for me, not a circle. I tried various
> radius settings, yet the figure definately has straight sides. Maybe I'm
> doing something wrong? This algorythm just fascinates me because I don't
> understand how it works and I don't have time at the moment to figure it
> out (have to run to a meeting).
>
> Thanks, Sean
>
> P.S. The BASIC code is given below:
>
> SCREEN 12
> WINDOW SCREEN (-100, 100)-(100, -100)
> radius = 50
> x = 0
> y = radius
> switch = 3 - 2 * radius
> LOP:
> PSET (x, y): PSET (x, -y): PSET (-x, y): PSET (-x, -y)
> PSET (y, x): PSET (y, -x): PSET (-y, x): PSET (-y, -x)
> IF switch < 0 THEN switch = switch + 4 * x + 6 ELSE switch = switch + 4 *
> (x - y) + 10
> y = y - 1
> x = x + 1
> IF x <= y THEN GOTO LOP

I'm not sure (I haven't tried it in other words), but I believe the y=y-1
statement should be part of the ELSE block that is computing 'switch =
switch + 4 * (x - y) + 10'. If you look at Andy's code, that line (i.e.
the y=y-1 line) is indented to the same level.

Scott