ZEND PHP 5 Certification STUDY GUIDE

54 ” Arrays
echo isset ($a[’a’]); // True
echo isset ($a[’c’]); // False
However, isset() has the major drawback of considering an element whose value is
NULL—which is perfectly valid—as inexistent:
$a = array (’a’ => NULL, ’b’ => 2);
echo isset ($a[’a’]); // False
The correct way to determine whether an array element exists is to use
array_key_exists() instead:
$a = array (’a’ => NULL, ’b’ => 2);
echo array_key_exists (’a’, $a); // True
Obviously, neither these functions will allow you to determine whether an element
with a given value exists in an array—this is, instead, performed by the in_array()
function:
$a = array (’a’ => NULL, ’b’ => 2);
echo in_array (2, $a); // True
Finally, an element can be deleted from an array by unsetting it:
$a = array (’a’ => NULL, ’b’ => 2);
unset ($a[’b’]);
echo in_array ($a, 2); // False
Licensed to 482634 - Amber Barrow (itsadmin@deakin.edu.au)
Flipping and Reversing
There are two functions that have rather confusing names and that are sometimes
misused: array_flip() and array_reverse(). The first of these two functions inverts
the value of each element of an array with its key: