Checar un elemento con particular Key

<?php

$meals = array('Walnut Bun' => 1,

               'Cashew Nuts and White Mushrooms' => 4.95,

               'Dried Mulberries' => 3.00,

               'Eggplant with Chili Sauce' => 6.50,

               'Shrimp Puffs' => 0); // Shrimp Puffs are free!

$books = array("The Eater's Guide to Chinese Characters",

               'How to Cook and Eat in Chinese');



// This is true

if (array_key_exists('Shrimp Puffs',$meals)) {

    print "Yes, we have Shrimp Puffs";

}

// This is false

if (array_key_exists('Steak Sandwich',$meals)) {

    print "We have a Steak Sandwich";

}

// This is true

if (array_key_exists(1, $books)) {

    print "Element 1 is How to Cook in Eat in Chinese";

}

?>