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I'm trying to create a PHP script that checks whether a number is a prime number or not. Just because I'm bored. But I can't get it to work properly. This is what I've written:

\n
for($i = $_GET["number"]; $i <= ($_GET["number"] / 2); $i++) {
if(($_GET["number"] % $i) == 0) { $yes = true; break;
} } } ?> Prime number counter

Prime number counter





if(isset($_GET["number"])) { echo "Last number: "; if($yes)
{ echo "Prime number!"; } else { echo "Not a prime number."; } } ?>

Enter a number and press 'check'
to check if it is a prime number.

\n

I get no errors, but it's not working right. It says that all numbers above zero aren't prime numbers and that all numbers below or exact zero are prime numbers. What is wrong?
Edit: Yes, I have to write $_GET["number"] instead of $number, because of some weird setting somewhere.
08.03.04 15:06
Post #1		Last edited: 08.03.04 15:08 (Dingbats - 2 times) [Softbrain Games] [Hide Sig (2)] [Profile] [Quote]
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y'know when it says the form action is prime.php? shouldn't it be $PHP_SELF ?
08.03.04 16:06
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The last iteration of your for loop will always return yes as true. It needs to be less than, not thes than or equal to :)

And if this hasn't been posted already while I've been pondering over it, no it doesn't need to be $PHP_SELF, providing the page that script is on is called prime.php. It only really needs to be $PHP_SELF if he's changing the page name all the time.

edit: lol managed to post that 8 times in a row. Must be something wrong wit the double post checker.

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08.03.04 16:34
Post #3		Last edited: 08.03.04 16:39 (ZoGgEr! - 1 times) [Hide Sig (8)] [Profile] [Quote]
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I'll try it. And yep, the page is called prime.php.
Edit: No, it still doesn't work. :( Anyone else?
08.03.04 17:39
Post #4		Last edited: 08.03.04 17:46 (Dingbats - 1 times) [Softbrain Games] [Hide Sig (2)] [Profile] [Quote]
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oh it's divided by two... hmm...

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08.03.04 17:56
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Yep, it is. Since eg. 183/182 can't be working, get it?
08.03.04 17:58
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\n
<?PHP\n

        for($i = $_GET["number"]; $i <= ($_GET["number"] / 2); $i++)<br />
\n?>
\n
should be
\n
<?PHP\n
for($i = $_GET["number"]; $i >= ($_GET["number"] / 2); $i--)
\n?>
\n

corse thats untested and only what i see at first glance
08.03.04 22:58
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wtf is a prime # counter? And what's the point of it? Help in math class lol?
09.03.04 04:29
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You know prime numbers right? Well this lets you type in a number and tells you if it is a prime number or not.

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09.03.04 07:49
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Thanks, Pope! Didn't think of that. Edit: WTF!!! It didn't work. Anyone else, please?:?
09.03.04 18:32
Post #10		Last edited: 09.03.04 18:34 (Dingbats - 1 times) [Softbrain Games] [Hide Sig (2)] [Profile] [Quote]
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Yes but what's the point pope. I kinda knew that part.
09.03.04 21:13
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Dingbats explained he felt bored and so decided to code something interesting. There was no actual reason.

I wish ppl would read threads fully...

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09.03.04 21:24
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Ah, i didnt see the text at the top of the code.
09.03.04 21:24
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HELPHELPHELPHELPHEL PNOW!1!1!
No, seriously. I've tried to change \n
for($i = $_GET["number"]; $i <= ($_GET["number"] / 2); $i++)
\n to \n
for($i = 0; $i <= ($_GET["number"] / 2); $i++)
\n, but that didn't work either. Please, can anyone help me?
10.03.04 18:41
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so if i'm following this script right, it tries to divide the number by all numbers less than it up to half it's value to see if you get whole number division, seems about right. I'd do it like this:

\n
<?PHP\n
$num = $_GET['number'];
for ($i=ceil($num/2);$i>1;$i--) {
if (($num % $i) == 0) {
$factor = true;
break;
}
}
$msg = ($factor) ? 'Sorry, not prime' : 'Wahey! Prime number' ;

\n?>
\n


FOOTNOTE:

if you need to use $_GET, then $PHP_SELF wont work either.

needs to be $_SERVER['PHP_SELF'] since register globals is off. This is a much better way to work btw - avoid any variable conflicts between GET vars and SESSION vars for example - always use superglobals.

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10.03.04 22:17
Post #15		Last edited: 10.03.04 22:22 (ReadMe - 1 times) [Hide Sig (7)] [Profile] [Quote]
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