Boolean / PHP: why does "bool(1) > $v" result in NULL?

Question

Saw this question on Toptal and got a little confused:

$v = 1;
$m = 2;
$l = 3;

if ($l > $m > $v) {
    echo "yes";
}
else {
    echo "no";
}

I get why the answer is "no", but their reasoning was a bit confusing to me:

First, $l > $m will be evaluated which yields a boolean value of 1 or true. Comparing that boolean value to the integer value 1 (i.e., bool(1) > $v) will result in NULL, so the output will be “no”.

Why does bool(1) > $v become null and not undefined or false?

@Rizier123 Are you saying "bool(1) > $v" will return "false" instead of NULL? So is their reasoning on Toptal not correct? — Etep, Jul 28 '16 at 21:12
Just because someone said something doesn't mean it's true... — FirstOne, Jul 28 '16 at 21:12

Lightness Races in Orbit · Accepted Answer · 2016-07-28T21:21:20.037

7

It doesn't. true > 1 is false (because they are instead "equal").

Furthermore, the entire program will not run because the "double conditional" is a parse error.

The answer you read is wrong.

This is why you shouldn't take advice from random strangers on the internet. Including me. ;)

edited Jul 28 '16 at 21:21

answered Jul 28 '16 at 21:11

Lightness Races in Orbit

378,754
76
643
1,055

Thank you. That's what I thought but I just wanted to double check :D! – Etep Jul 28 '16 at 21:14
@PeteKang See: http://stackoverflow.com/q/80646/3933332 and know that `<`/`>` does a loosely comparison. – Rizier123 Jul 28 '16 at 21:17
1

@Rizier123: Those pipe-based ASCII tables are glorious! – Lightness Races in Orbit Jul 28 '16 at 21:17
@LightnessRacesinOrbit I used: [this site](http://www.sensefulsolutions.com/2010/10/format-text-as-table.html) to do it, but it seems to be broken right now, so you can use it from [the past](https://web.archive.org/web/20150413065746/http://www.sensefulsolutions.com/2010/10/format-text-as-table.html) – Rizier123 Jul 28 '16 at 21:20
@Rizier123: Oh, so you cheated! (They have a JS error) – Lightness Races in Orbit Jul 28 '16 at 21:22
@LightnessRacesinOrbit I wouldn't call that cheating. People who use "hidden" characters to get around the minimal character limit [for an answer](http://meta.stackoverflow.com/a/285644/3933332), that is what I would call cheating :P – Rizier123 Jul 28 '16 at 21:28
@Rizier123: Deleted posts obviously do not count. – Lightness Races in Orbit Jul 29 '16 at 09:04
@LightnessRacesinOrbit That [one](http://stackoverflow.com/a/32655927/3933332) still counts. (Why was the other one deleted by a mod?) – Rizier123 Jul 29 '16 at 09:08
@Rizier123: Cos it was crap, useless and late to the party. And mods hate that. :) – Lightness Races in Orbit Jul 29 '16 at 09:23

score 1 · Answer 2 · answered Jul 28 '16 at 21:18

Just for the record

<?php

$v = 1;
$m = 2;
$l = 3;

var_export( $l > $m ); // true
var_export( $m > $v ); // true
var_export( $l > ($m > $v) ); // false: (3 > true) = false
var_export( ($l > $m) > $v ); // false: (true > 1) = false
var_export( $l > $m > $v ); // parse error

Boolean / PHP: why does "bool(1) > $v" result in NULL?

2 Answers2