Until False * Not Sleep(30) ?????

[kylomas]

I found this stmt in a GDI+ example that I was looking at and do NOT understand it. Can someone explain it please?

Until False * Not Sleep(30)

Thanks,

kylomas

[water]

It always evaluates to 0. Sleep(30) returns 1. Not Sleep(30) therefore evaluates to 0. False = 0. So 0 * 0 = 0.

There must be a statement in the Do Until loop to exit the loop.

Edited November 28, 2011 by water

[kylomas]

water,

Yes, that is how I interpreted it but thought that I must be missing something. Why not just code "until 1"?

This is the entire loop (forgot which thread I got it from)

Do
_GDIPlus_GraphicsClear($backbuffer, 0x90000000)
For $x = 1 To UBound($arrTxt1) - 1
  $x1 = $width_mul_045 + Cos(($i + $m) * $pi_div_180) * $radius_x1
  $y1 = $height_mul_045 + Sin(($i + $m) * $pi_div_180) * $radius_y1 - $fontsize_txt1 / 4
  $arrX1[$x] = $x1
  $arrY1[$x] = $y1
  DllStructSetData($tLayout, "x", $arrX1[$x])
  DllStructSetData($tLayout, "y", $arrY1[$x])
  _GDIPlus_GraphicsDrawStringEx($backbuffer, $arrTxt1[$x], $hFont1, $tLayout, $hFormat, $brush1[$x])
  $m += $a
Next
For $x = 1 To UBound($arrTxt2) - 1
  $x2 = $width_mul_045 + Cos(($j + $n) * $pi_div_180) * $radius_x2 * Cos($y * $pi_div_180)
  $y2 = $height_mul_045 + Sin(($j + $n) * $pi_div_180) * $radius_y2 - $fontsize_txt2 / 4
  $arrX2[$x] = $x2
  $arrY2[$x] = $y2
  DllStructSetData($tLayout, "x", $arrX2[$x])
  DllStructSetData($tLayout, "y", $arrY2[$x])
  _GDIPlus_GraphicsDrawStringEx($backbuffer, $arrTxt2[$x], $hFont2, $tLayout, $hFormat, $brush2[$x])
  $n += $b
Next
If Mod($y, 2) = 1 Then Array_Shift($brush2, 1)
$y += 1
_GDIPlus_GraphicsDrawImageRect($graphics, $bitmap, 0, 0, $width, $height)
$i += 1
;~  If $i >= 360 Then
;~   $i = 0
;~   $m = 0
;~  EndIf
$j -= 2
;~  If $j <= 0 Then
;~   $j = 360
;~   $n = 0
;~  EndIf
Until False * Not Sleep(30)

kylomas

[water]

Because the Do Until statement is evaluated at the end of the loop until the expression is true. Until 1 would end the loop after 1 round. Until 0 loops forever and therefore needs a statement in the loop to exit.

"Do Until 0" is nearly the same as "While 1 WEnd". The only difference is that the expression is evaluated at the beginning of the loop.

Therefore the statements in a While loop could never be executed whereas the statements in an Until loop are at least executed once.

[kylomas]

water,

Yes, my mistake, my point, however, remains. What is the purpose of the multiplication on a sleep stmt? That is what got me to believe that I was missing something. This code is from "rotating letters" by UEZ, perhaps he could offer some input???

kylomas

[water]

Maybe what we are doing here was intended. Looks like some kind of obfuscation.

[water]

What I don't understand is how the loop ever ends. There is no exit statement in the code you posted.

[BrewManNH]

Looks like he was putting a sleep into the loop and at the same time making it an endless loop.

[UEZ]

Let me try to explain

Until False * Not Sleep(30) is the same as

Do

Sleep(30)

Until False

False is the expression and the expression is tested after the loop is executed. That means as water already mentioned Sleep(30) will be execute and Sleep() returns always True but the Not negate it to false. 0 * 0 is always 0 which is equivalent to False.

The loop never ends. Exit code is handled by GUIOnEventMode.

Br,

UEZ

[water]

Thanks for shedding some light on the subject!

[kylomas]

UEZ,

Very clever, thanks for the explanation...

kylomas