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Validate User Input

P: 8
Hey all!

I am making a very simple program which requires the user to enter a numerical value into a text box (html form) and then multiplies it by 10 before echoing back. The program is working fine.

However, when I enter some letters, php returns an ugly error. Is there a way to prevent the user from entering letters?

Thanks!
Dec 22 '07 #1
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Markus
Expert 5K+
P: 6,050
This was a little learning curve for me. So thanks for letting me help you :D!

I'll start with the code:
[php]
<?php

$stringGood = "2345634545156456";
$stringBad = "32873428473t30984";

$pattern = '/[^0-9]/'; //pattern for regular expression
if(preg_match($pattern, $stringBad)){
echo "String: $stringBad, contained characters <em>other than</em> numbers.";
} else {
echo "String was good.";
}

echo "<br /><br />

if(preg_match($pattern, $stringGood)){
echo "String: <strong>$stringGood</strong>, contained characters <em>other than</em> numbers.";
} else {
echo "String was good.";
}

?>
[/php]
You better read this!
First we start off with the strings we are going to check ($stringGood, $stringBad) named like so for obvious reasons ;) - i assume you'll need to change the variables to something like:
[php]
$string = $_POST['number'];
[/php]
The next thing ($patter) is the pattern we will use for the regular expression, and don't be worried if these scare you - they scare me! But once you try it for yourself they aren't too ghastly.
Basically what the pattern is saying is:
[start pattern ^check for something that is NOT 0-9included in this part ]end pattern.
So we're checking for anything that is not within the scope of 0, 1, 2...
Easy eh?
Next we're onto the preg_match. What this does is check the given subject for any given regular expression. Great. Exactly what we need.
If the given expression is found in the given subject; it will return 1 / true. And i bet you can tell me what it returns if it isn't found? ;)
So so:
[php]
if(preg_match returns TRUE){
//pattern was found - execute code.
} else {
//pattern not found - execute code.
}
[/php]

Hope this long winded solution helps!

Any questions just post back :)

markus.
Dec 22 '07 #2

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