Associative Arrays

Keeping track of array elements by index works just fine, but can require extra work in terms of remembering which number refers to which product. It can also make code hard for other programmers to follow.
This is where associative arrays come into their own. Using them, you can reference the items in an array by name rather than by number. Following Example expands on the previous code by giving each element in the array an identifying name and a longer, more explanatory string value.

$paper['copier'] = "Copier & Multipurpose";
$paper['inkjet'] = "Inkjet Printer";
$paper['laser'] = "Laser Printer";
$paper['photo'] = "Photographic Paper";
echo $paper['laser'];

In place of a number (which doesn’t convey any useful information, aside from the position of the item in the array), each item now has a unique name that you can use to reference it elsewhere, as with the echo statement—which simply prints out Laser Printer. The names (copier, inkjet, and so on) are called indexes or keys and the items assigned to them (such as “Laser Printer”) are called values.
This very powerful feature of PHP is often used when extracting information from XML and HTML. For example, an HTML parser such as those used by a search engine could place all the elements of a web page into an associative array whose names reflect the page’s structure:

$html['title'] = "My web page";
$html['body'] = "... body of web page ...";