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Why is this expression used in the tutorial?

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In the lesson on PHP Filters in the code sample "Validate an Integer" there is the following code:

$int = 100;

if (!filter_var($int, FILTER_VALIDATE_INT) === false) {
    echo("Integer is valid");
} else {
    echo("Integer is not valid");

Why use this expression:

(!filter_var($int, FILTER_VALIDATE_INT) === false)

instead of what seems to me to be the more logical expression?:

  (filter_var($int, FILTER_VALIDATE_INT) === true)


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filter_var() with the FILTER_VALIDATE_INT filter returns an integer, not true, so === true will always fail. By using The ! operator, they transform it into a boolean. This boolean, for any integer other than zero, is always false. This solution doesn't account for the integer zero which converts to true, but W3Schools also has a section talking about that.

They could just use !!filter_var() or (bool)filter_var() and they wouldn't need the === false part. This would still not solve the integer zero problem, though.

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