PHP: If statement issue

Question

The array resAlloc contains 10 columns and 5 rows. All entries are equal to 0. So, I expect the following IF statement be TRUE, but it's false for some reason... Why?

if ($resAlloc[$i][$j] != 'ts' && $resAlloc[$i][$j] != 't' && $resAlloc[$i][$j] != 'st') {
    $count++;
}

Samy Dindane · Accepted Answer · 2012-05-19 22:16:54Z

3

!= evaluates 0 as false. Use !== which is more strict.

answered May 19, 2012 at 22:16

Samy Dindane

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5 Comments

octern Over a year ago

How does that explain the problem? 0!='ts' and false!='ts' should both evaluate to true, and so the if statement as a whole should be true.

octern Over a year ago

Right, but I don't understand why any of the comparisons would evaluate to false just based on the fact that != treats 0 as false. ... Oh, this is an issue of order of operations, isn't it? The OP probably wanted the three != comparisons to be evaluated before the && operations, and that's probably not what's happening.

octern Over a year ago

There's a completely separate issue, which is that 0 != 'any string' also evaluates to false (see my answer below).

octern Over a year ago

I don't think you were downvoted. I upvoted you for a minute and then removed the upvote when I realized that I didn't understand your answer, and then I did comment. I'll upvote you again if one of us manages to straighten me out.

octern Over a year ago

Sorry about the serial commenting; I should have added that the problem I mentioned actually would be addressed by your suggestion to use strict comparison. And they're kind of the same problem after all.

alexpja · Accepted Answer · 2012-05-19 22:16:13Z

0

IIRC anything equaling 0 with != will return FALSE.

answered May 19, 2012 at 22:16

alexpja

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2 Comments

octern Over a year ago

That's not correct. 0!=1 returns true (thank heavens!). I think this is an issue with comparing strings to integers -- strings get cast to the integer zero, so the two end up being equal after all!

alexpja Over a year ago

I said IIRC, wasn't sure exactly.

octern · Accepted Answer · 2012-05-19 22:49:50Z

0

The problem is that you're comparing a string and an integer, and PHP is "helpfully" casting the string to an integer -- the integer zero. 0!='ts' evaluates as false, because the comparison it ends up doing after conversion is 0!=0. You can prevent this by explicitly treating the contents of your array as a string:

strval($resAlloc[$i][$j]) != 'ts'

This will do the comparison '0'!='ts', which correctly evaluates to true. If you pass strval() a string it returns it unchanged, so this should be safe to use regardless of what's in your array.

Alternately, as Samy Dindane said, you can just use !== which won't do any type conversion.

edited May 19, 2012 at 22:49

answered May 19, 2012 at 22:43

octern

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