Making sense of inequality comparisons between a number and a boolean

Question

The type comparison chart in PHP documentation shows the result of both strict === and loose == comparisons. There is nothing about inequality comparisons:

true < 0 => false
0 < true => true
true < 1 => false
1 < true => false
true < -1 => false
-1 < true => false

false < 0 => false
0 < false => false
false < 1 => true
1 < false => false
false < -1 => true
-1 < false => false

Can someone rationalize the above results?

score 1 · Answer 1 · 2013-09-03T10:54:57.743

1

when converting booleans to integer, the true will be converted to 1 and false to 0

From PHP Manual: http://php.net/manual/en/language.types.integer.php

From booleans

FALSE will yield 0 (zero), and TRUE will yield 1 (one).

Also:

-1 is considered TRUE, like any other non-zero (whether negative or positive) number!

true  < 0 => false => true < (bool)(0) => true < false => 1 < 0 = false
0 < true => true  => (bool)(0) < true => false < true => 0 < 1 = true
true < 1 => false => true < (bool)(1) => true < true => 1 < 1 = false
1 < true => false => (bool)(1) < true => => true < true => 1 < 1 = false
true < -1 => false => true < (bool)(-1) => true < true => 1 < 1 = false
-1 < true => false => (bool)(-1) < true => true < true = > 1 < 1 = false

false < 0 => false => false < (bool)(0) => false < false => 0 < 0 = false
0 < false => false => (bool)(0) < false => false < false => 0 < 0 = false
false < 1 => true => false < (bool)(1) => false < true => 0 < 1 = true
1 < false => false => (bool)(1) < false => true < false => 1 < 0 = false
false < -1 => true => false < (bool)(-1) => false < true => 0 < 1 = true
-1 < false => false => (bool)(-1) <  false => true < false => 1 < 0 =  false

edited Sep 03 '13 at 10:54

answered Sep 03 '13 at 06:29

Should be `-1 < true => false => bool(-1)=true < true = false` By the way, where does it says that `true > false`? Thanks :) – Question Overflow Sep 03 '13 at 06:54
because bool will be cast as integer by default so that true is 1 and false is 0 and logically, true should be greater than false... – Sep 03 '13 at 07:07
Hey, I just realise that your answer is still not correct. It doesn't work for `false < -1 => true` – Question Overflow Sep 03 '13 at 08:19
yes, you are right I get the correct answer, I will update this post soon. – Sep 03 '13 at 09:04
In your initial answer, the left hand side variable is cast to match the type on the right hand side. Now the numeral is cast to boolean. I need to know where you get the basis for this. Is it written somewhere in the document? How do you know? – Question Overflow Sep 03 '13 at 12:16

score 0 · Answer 2 · answered Sep 03 '13 at 07:13

true < 0 => false ===> 1 < 0 => false (0==0 ==>true )
0 < true => true ===> 0 < 1 => true
true < 1 => false ===> 1 < 1 => false (1==1 ==>true )
1 < true => false ===> 1 < 1 => false (1==1 ==>true )
true < -1 => false ===> 1 < -1 => false
-1 < true => false ===> -1 < 1 => false ======> 1 < 1 => false (boolean type is treated as unsigned)
===> false < 0 => false ===> 0 < 0 => false
0 < false => false ===> 0 < 0 => false
false < 1 => true ===> 0 < 1 => true
1 < false => false ===> 1 < 0 => false
false < -1 => true ===> 0 < -1 => true ======> 0 < 1 => true(boolean type is treated as unsigned)
-1 < false => false ===> -1 < 0 => false ======> 1 < 0=> false(boolean type is treated as unsigned)

Can you provide some basis for your answer? – Question Overflow Sep 03 '13 at 08:22 — Question Overflow, Sep 03 '13 at 08:22

Making sense of inequality comparisons between a number and a boolean

2 Answers2