how to restrict a text box to nly accepting numbers

[masterofwee]

I'm writing a calculator to solve this formula, and I need a way to restrict all the textboxes on my form to only accept numbers. How can I do this with php?

[DarkWater]

<?php
$input = $_POST['field'];
if (!ctype_digit($input)) {
    echo "Input must only be a digit!";
}
?>

 

Now, just letting you know, you wouldn't really use it like that.  You'd implement it in a larger scheme, but this was just an example.