Programming PHP

Identifying Elements of an Array
You can access specific values from an array using the array variable’s name, followed
by the element’s key (sometimes called the index) within square brackets:
$age['Fred']
$shows[2]
The key can be either a string or an integer. String values that are equivalent to integer
numbers (without leading zeros) are treated as integers. Thus, $array[3] and
$array['3'] reference the same element, but $array['03'] references a different element.
Negative numbers are valid keys, and they don’t specify positions from the
end of the array as they do in Perl.
You don’t have to quote single-word strings. For instance, $age['Fred'] is the same
as $age[Fred]. However, it’s considered good PHP style to always use quotes,
because quoteless keys are indistinguishable from constants. When you use a constant
as an unquoted index, PHP uses the value of the constant as the index:
define('index',5);
echo $array[index]; // retrieves $array[5], not $array['index'];
You must use quotes if you’re using interpolation to build the array index:
$age["Clone$number"]
However, don’t quote the key if you’re interpolating an array lookup:
// these are wrong
print "Hello, $person['name']";
print "Hello, $person["name"]";
// this is right
print "Hello, $person[name]";
Storing Data in Arrays
Storing a value in an array will create the array if it didn’t already exist, but trying to
retrieve a value from an array that hasn’t been defined yet won’t create the array. For
example:
// $addresses not defined before this point
echo $addresses[0]; // prints nothing
echo $addresses; // prints nothing
$addresses[0] = 'spam@cyberpromo.net';
echo $addresses; // prints "Array"
Using simple assignment to initialize an array in your program leads to code like this:
$addresses[0] = 'spam@cyberpromo.net';
$addresses[1] = 'abuse@example.com';
$addresses[2] = 'root@example.com';
// ...
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