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PHP Build a Simple PHP Application Creating the Menu and Footer Introducing Conditionals

Posted by Timothy McCune
Timothy McCune
6,744 Points

How come we are using 'AND' instead of '&&'?

I understand that php technically allows the use of AND in conditionals, but it will be deprecated eventually. Using AND to teach the idea of conditionals may make sense, teaching the use of the AND(&&) & OR(||) operator, right off the bat, would avoid any confusion later.

Although there may not seem like there is much of a difference between AND and && -or- OR and || but there are big differences between them. && has a higher precedence over AND. Likewise || has a higher precedence over OR. Take the following example:

// Example #1 $foo = true; $bar = false;

$foobar = $foo and $bar;

You would expect that $foobar would equal false, but surprisingly it would equal true. Why you ask? the = sign has a higher precedence than and therefore php would interpret the above example as: ($foobar = $foo) and $bar;

instead of what we would expect it to do: $foobar = ($foo and $bar);

// Example #2 $foo = true; $bar = false;

$foobar = $foo && $bar; // equals false

The above example works as expected (AND how we hoped the first example would work)

I realize that this lesson is a mere introduction to conditionals in PHP, But wouldn't you agree that it is a good idea to teach good habits from the beginning, rather than introducing bad habits and having them change it later.

Thanks, Tim

Zachary Green
Zachary Green
16,359 Points
Zachary Green
Zachary Green
16,359 Points

I understand where your coming from. I would guess that the staff just want to be able to assoc AND with && and OR with ||. They do a great job of giving us all the tools but its up to us to use the correct ones in our real world applications.

Marcus Parsons
Marcus Parsons
15,719 Points

+1 Zachary.

1 Answer

Alena Holligan
STAFF
Alena Holligan
Treehouse Teacher
Alena Holligan
Alena Holligan
Treehouse Teacher

They are both valid. There's the possibility false assignment when using AND as opposed to &&. AND has a lower precedence than &&. So, when having a conditional

<?php $x && $y || $z; ?>
<?php $x AND $y || $z; ?>

In the latter, we're actually executing x and (y or z) since || has a higher precedence then AND.

Now you may say, why not just swap || with OR. Well here's another example of this failing

<?php 
  $x = true;
  $y = false;
  $seekingTheTruth = $x and $y;
?>

In this example we can expect the value to return true. This is because the equal operator has higher precedence: ($seekingTheTruth = $x) and $y;

http://php.net/manual/en/language.operators.php