Question about +=

[alexjewell]

A friend of mine saw "+=" in a script and asked me what it meant.
I searched php.net and google and everything, and I've come up empty handed.
"plus equals"???
I don't get it.
Explain?

[blm126]

Here is an example

<?php
$num = 5;
$num += 10;
echo $num
?>

that will produce 15. it is equivalent to

<?php
$num = 5;
$num =  $num + 10;
echo $num
?>