What does the *= operator do?

Question

I've been looking through a few mock exams and study guides for PHP and I came across this example:

$a = array(1, 2, 3);
foreach ($a as $x)
    $x *= 2;
echo $a[0]  * $a[1]  * $a[2];

This returns 6.

My question is: what exactly does the *= operator mean?

[What does this symbol mean in PHP](http://stackoverflow.com/questions/3737139/reference-what-does-this-symbol-mean-in-php) — Mark Baker, Jun 27 '13 at 09:45
This example is really really bad as a teaching tool (it's either misguided or trying to show that non-reference `foreach` does not make changes stick -- in which case, why confuse the student with extra multiplications after the loop that have nothing to do with making that point?). Beware of that study guide. — Jon, Jun 27 '13 at 09:50
I don't see who uvoted this question. This really doesn't show any research effort at all. — Aleph, Jun 27 '13 at 09:51
@AnotherTest I challenge you to Google a symbol like this. You won't find anything useful. — Danny Beckett, Jun 27 '13 at 09:51
`$a*=b$ $a-=$b $a+=$b $a/=$b ....` == ` $a= $a*$b, $a= $a-$b, $a= $a+$b, $a= $a/$b, ` — Robert, Jun 27 '13 at 09:52
This is covered in the [PHP language reference](http://www.php.net/manual/en/language.operators.assignment.php): *"In addition to the basic assignment operator, there are "combined operators" for all of the [binary arithmetic](http://www.php.net/manual/en/language.operators.php), array union and string operators that allow you to use a value in an expression and then set its value to the result of that expression."* Though I understand that it might not be easy to find if you don't know what to look for (*assignment* is the keyword here). — Felix Kling, Jun 27 '13 at 09:52
@DannyBeckett: Go to Google and start typing `php *=`. You do not even have to know the term "operator". — Jon, Jun 27 '13 at 09:52
@DannyBeckett Who said anything about google? http://php.net/manual/en/language.operators.assignment.php — Aleph, Jun 27 '13 at 09:53
The study guide comes from Zend, I wasn't particularly interested in doing the exam I just wanted to have an idea of what kind of knowledge they would expect to pass it. — Philip Richardson, Jun 27 '13 at 09:53
@AnotherTest If you're trying to find something out, you'd typically Google it. Searching for something like `php *=` yields utter crap. — Danny Beckett, Jun 27 '13 at 09:54
@DannyBeckett If it's something related to the PHP core language, it'd typically search php.net. — Aleph, Jun 27 '13 at 09:56
@Jon Again, utter crap: [https://www.google.co.uk/search?q=php+*%3D+operator](https://www.google.co.uk/search?q=php+*%3D+operator) — Danny Beckett, Jun 27 '13 at 09:56
@AnotherTest **Good luck search php.net!** http://uk1.php.net/results.php?q=%2A%3D&l=en&p=all — Danny Beckett, Jun 27 '13 at 09:57
@DannyBeckett He said "operator" in the question. So anyone would search for "operator" on the online documentation. — Aleph, Jun 27 '13 at 09:58
People, my point here is: trying to find out what a symbol does, in any language, inherently takes the mickey. — Danny Beckett, Jun 27 '13 at 09:58

score 3 · Answer 1 · edited Jun 27 '13 at 09:53

3

$x *= 2;

is nothing but

$x = $x * 2;

edited Jun 27 '13 at 09:53

Mr. Alien

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answered Jun 27 '13 at 09:47

Yogesh Suthar

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Stefano Sanfilippo · Accepted Answer · 2013-06-27T09:53:29.987

It's a shortcut for:

$x = $x * 2

A syntax which dates back to C and accounts for natural (from a human's point of view) "multiply $x by 2", rather than programmatic "take $x value, multiply it by 2 and reassign back to $x" -- as Kernighan and Ritchie stated in their The C programming language.

It can be applied to all numerical operators:

$x = $x + 2 <---> $x += 2
$x = $x - 2 <---> $x -= 2
$x = $x / 2 <---> $x /= 2
etc...

By the way, the printed value 6 it's not related.

score 1 · Answer 3 · edited Jun 27 '13 at 09:57

1

$x *= 2; is the same as $x = $x * 2; (like += and -= and .= etc)

edited Jun 27 '13 at 09:57

HamZa

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answered Jun 27 '13 at 09:47

Imane Fateh

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score 1 · Answer 4 · edited Jun 27 '13 at 09:49

1

+=, *=, /= and -= are compound operators. In your code, it would expand to:

$x = $x * 2

edited Jun 27 '13 at 09:49

Danny Beckett

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answered Jun 27 '13 at 09:48

SBI

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What does the *= operator do?

4 Answers4