> -----Original Message-----
> From: Lazor, Ed [mailto:[EMAIL PROTECTED]]
> Sent: 17 June 2002 21:24
> To: 'Chris Knipe'; [EMAIL PROTECTED]
> Subject: RE: [PHP] substr?
>
>
> Here's another way of writing that code that may be easier to
> work with:
>
> $TestValues = array("072", "073", "082", "083", "084");
> $NumC = $substr($_POST['NumC'], 0, 3);
> if (in_array($NumC, $TestValues))
> $FormError = "True";
And here's another:
switch substr($_POST'NumC'], 0, 3):
case '072':
case '073':
case '082':
case '083':
case '084':
// acceptable -- do anything appropriate here
// (even nothing, if that's what you want!)
break;
default:
// not acceptable
$FormError = "True";
endswitch;
Incidentally, why are you setting the variable $FormError to the string "True", rather
than the Boolean TRUE? You may have a perfectly ggod reason, but it looks odd to my
eyes. If a Boolean would be acceptable, you could also write it like this:
$NumC = substr($_POST'NumC'], 0, 3);
$FormError = $NumC!='072' && $NumC!='073'
&& $NumC!='082' && $NumC!='083' && $NumC!='084';
or:
$FormError = !in_array(substr($_POST'NumC'], 0, 3),
array('072', '073', '082', '083', '084'));
> > -----Original Message-----
> > From: Chris Knipe [mailto:[EMAIL PROTECTED]]
> > Sent: Monday, June 17, 2002 12:19 PM
> >
> > So what's the difference between
> > if (!(($blah == blah) OR ($ab == ab))) {
> > and
> > if ((!$blah == blah) OR (!$ab == ab)) {
Well, as you've written it, a hell of a lot!! I assume you meant the second version
to be:
if (!($blah == blah) OR !($ab == ab)) {
> > Shouldn't they both do the same? And if so, why didn't they
> > in this case??
No, they absolutely shouldn't. Think about it: the first ORs the two comparisons, and
then takes the NOT of that; the second NOTs both comparisoons, then does the OR. It's
the same sort of reason why
$x = -1 * -2;
is not the same as
$x = -(1 * 2);
When working with Boolean expressions in this way, deMorgan's laws often come in
handy; these state that:
!a AND !b is the same as !(a OR b)
!a OR !b is the same as !(a AND b)
Hope this helps!!
Cheers!
Mike
---------------------------------------------------------------------
Mike Ford, Electronic Information Services Adviser,
Learning Support Services, Learning & Information Services,
JG125, James Graham Building, Leeds Metropolitan University,
Beckett Park, LEEDS, LS6 3QS, United Kingdom
Email: [EMAIL PROTECTED]
Tel: +44 113 283 2600 extn 4730 Fax: +44 113 283 3211
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