Why am I getting a division by zero error here?

Question

I'm getting a division by zero error on this line of code:

$ratio['p{W}'] = ($ratio['{W}'] === 0) ? 0 : ($colorTotal === 0) ? 0 : ($ratio['{W}'] / $colorTotal) * 100;

I've tested the above with:

echo '$ratio[{W}]:'.$ratio['{W}'].', $colorTotal:'.$colorTotal;

if($ratio['{W}'] === 0) {
    echo('$ratio[{W}]: zero');
}
else {
    echo('$ratio[{W}]: not zero');
}

if($colorTotal === 0) {
    echo('$colorTotal: zero');
}
else {
    echo('$colorTotal: not zero');
}

and the results are:

[01-Jul-2015 17:40:26 UTC] $ratio[{W}]:0, $colorTotal:0

[01-Jul-2015 17:40:26 UTC] $ratio[{W}]: zero

[01-Jul-2015 17:40:26 UTC] $colorTotal: zero

It seems I should never reach this point ($ratio['{W}'] / $colorTotal) in the code since the previous criteria is 0 in the checks but it seems to reach it? How can I prevent this error?

Ternary operator http://stackoverflow.com/questions/17981723/how-to-write-a-php-ternary-operator — Asif Mushtaq, Jul 01 '15 at 17:50
@AsifMushtaq: Sure, I can do an if else. I'm trying to understand why I get a division by zero in the above line of code. — Howard, Jul 01 '15 at 17:52
@ElGavilan: Can you explain what you mean by order of operations? — Howard, Jul 01 '15 at 17:53
@u_mulder: This question is about why I get a division by zero error when it seems I shouldn't since I'm checking before I try the division. — Howard, Jul 01 '15 at 17:54
Ternary operators are really handy but they are not easily readable when you nest them like this. — ElGavilan, Jul 01 '15 at 18:02

ElGavilan · Accepted Answer · 2015-07-01T18:04:52.917

3

Ternary operators are left-associative in PHP. Your code is equivalent to:

$ratio['p{W}'] = (($ratio['{W}'] === 0) ? 0 : ($colorTotal === 0)) ? 0 : ($ratio['{W}'] / $colorTotal) * 100;

meaning that ($ratio['{W}'] === 0) ? 0 : ($colorTotal === 0) evaluates first. The result of this is either 0 or true, meaning that the true part of the second ternary will always execute.

It looks to me like you probably want to make the whole expression right-associative:

$ratio['p{W}'] = ($ratio['{W}'] === 0) ? 0 : (($colorTotal === 0) ? 0 : ($ratio['{W}'] / $colorTotal) * 100);

edited Jul 01 '15 at 18:04

answered Jul 01 '15 at 17:57

ElGavilan

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You have to place the semicolon on the outside of the brackets but I'll choose yours as the answer. – Howard Jul 01 '15 at 18:04
That's what you get overusing ternary operators... 1 nesting level, and yet you're not sure exactly what happens... – Laurent S. Jul 01 '15 at 18:07
To be honest it's more due to my lack of understanding of ternary operators and the order of operation that was happening more than anything. I learned something new today. – Howard Jul 01 '15 at 18:09

Balmipour · Answer 2 · 2015-07-01T17:58:54.363

0

I'll start out by adding parenthesis around your ternaries, since I'm afraid ElGavilan is right. Your one-liner is quite ugly to read, and refers to code we don't have, which means we can't test your code.

I like ternaries... but not that way !

edited Jul 01 '15 at 17:58

answered Jul 01 '15 at 17:56

Balmipour

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parent::p is just echo I changed it to echo so it's easy to understand. – Howard Jul 01 '15 at 17:57
Plus one for *I like ternaries... but not that way*.. You are right, the ternary operator should be used to make the code *more* readable and not to make it *less* readable. – hek2mgl Jul 01 '15 at 18:01

score 0 · Answer 3 · answered Jul 01 '15 at 18:02

$ratio['p{W}'] = ($ratio['{W}'] === 0) ? 0 : ($colorTotal === 0) ? 0 : ($ratio['{W}'] / $colorTotal) * 100;

($ratio['{W}'] === 0) means $ratio['{W}'] is false then the false code ($colorTotal === 0) execute in the both cases ($ratio['{W}'] === 0) & ($colorTotal === 0) value became 0. Same for last case division case 0/0.

Why am I getting a division by zero error here?

3 Answers3