Noob Question.. what does ? character do in this statement

[Why_Not_Zoidberg]

So I am creating php script to make my navigation for a website. I've gathered bits and pieces from books/online forums. One thing that is confusing me is what does the "?" in this line accomplishes? 
 

$currentTitle=isset($mainMenu[$currentPage]) ? $mainMenu[$currentPage] : '';

As you can imagine this is a hard question to find an answer to because of the use of ?'s in <?php. Also a little confused on the : symbol also. I am writing this script to keep track of the current page to generate a css class to be modified, which works. But then I also thought id have it generate the titles too but when i echo this.. The script goes bad.
 

echo'
<title>
  ',(is_empty($currentTitle) ? '' : $currentTitle.' - '),$siteTitle,'
</title>
'

I would be grateful for any help! Thanks in advance.

[benanamen]

That is called a Ternary Operator. Same thing as if/else

 

https://davidwalsh.name/php-shorthand-if-else-ternary-operators

 

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

Edited February 4, 2016 by benanamen

[Why_Not_Zoidberg]

Thanks so much!