4

I am running a very simple if statement which works perfect until I add the two additional || (or) operators.

Here is my code:

if ($planDetails['Company']['name'] != 'company1'
|| $planDetails['PlanDetail']['name'] != 'pd-name1' 
|| $planDetails['PlanDetail']['name'] != 'pd-name2') { echo "TEST"; }

I've checked my array data and table values to ensure they are precise in the names etc.. And this is not kicking. What am I doing wrong? When I remove the additional 2 || options, the first argument works fine, so I know my logic is correct.

What in the name am I doing wrong here. Someone please set me straight!

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4
  • post a var_dump($planDetails); Commented Mar 4, 2011 at 20:30
  • Matt, my dump is much too large to sensibly post here, but I already checked that. The array contains the values I need and I am echoing them out simply by: echo $planDetails['PlanDetail']['name']; gets me the correct value on the requested page. Commented Mar 4, 2011 at 20:33
  • "this is not kicking" - Which means? I interpreted that as "it does not print out TEST", which is probably not what you meant. Commented Mar 4, 2011 at 20:52
  • Yes, Eric I meant it's not working as intended. The "TEST" should only echo if no matches are found. Commented Mar 4, 2011 at 21:00

3 Answers 3

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7

Well, what I read here is:

If $variable is not equal to A Or $variable is not equal to B
Then echo "TEST"

Since $variable cannot be equal to both A and B at the same time, it will always print "TEST".

Of course, the above refers to the last two conditions in your if.

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2 Comments

+1: It becomes clearer if you apply DeMorgan's Law and think of the statement as: If NOT($variable = A AND $variable = B). Then it's obvious that $variable cannot be both A and B simultaneously.
I'm getting a taste of this logic now. This really threw me a left curve as I now see how wrong I was. Thanks for the added clarification.
6

Your ors should be ands. The expression a != 1 || a != 2 is always true because whatever the value of a is, one or the other of the expressions will be true, so the final result will be true.

To fix, change || to &&.

I guess you made this mistake because you started with this expression and wanted to invert it:

if ($planDetails['Company']['name'] == 'company1'
|| $planDetails['PlanDetail']['name'] == 'pd-name1' 
|| $planDetails['PlanDetail']['name'] == 'pd-name2')

The simplest way to invert this expressions is as follows:

if (!($planDetails['Company']['name'] == 'company1'
|| $planDetails['PlanDetail']['name'] == 'pd-name1' 
|| $planDetails['PlanDetail']['name'] == 'pd-name2'))

Using this method, you don't need to do any complex boolean logic in your head to see that it works - it's just a simple negation of what you already know. Note that this is not the same as inverting the == to != individually. See De Morgan's Laws for more details.

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6

Please refer to De Morgan's laws.

NOT (P AND Q) = (NOT P) OR (NOT Q)
NOT (P OR Q) = (NOT P) AND (NOT Q)

You have:

(NOT P) OR (NOT Q) OR (NOT R)

Which is the same as:

NOT (P AND Q) OR (NOT R) => 
NOT (P AND Q AND R)

Therefore, P, Q, R must all be false to print "TEST". If one of them is true then you will not print "TEST".

I believe you want:

NOT (P OR Q OR R)

Which would be:

(NOT P) AND (NOT Q) AND (NOT R)

OR

if (!($planDetails['Company']['name'] == 'company1'
|| $planDetails['PlanDetail']['name'] == 'pd-name1' 
|| $planDetails['PlanDetail']['name'] == 'pd-name2'))
{ 
    echo "TEST"; 
}

AKA

if ($planDetails['Company']['name'] != 'company1'
&& $planDetails['PlanDetail']['name'] != 'pd-name1' 
&& $planDetails['PlanDetail']['name'] != 'pd-name2')
{ 
    echo "TEST"; 
}
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3 Comments

wow, that took me too long to type... it appears others have also posted similar answers
Dan, thanks very much for the added clarification. I see exactly what you are describing. My logic was extremely flawed.
Yes, that's why I put it first. It "reads" easier. For the fun of it, you could have put them in an array and do a contains (but worse performance): php.net/manual/en/function.in-array.php

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