5.2. Identifying Elements of an Array
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 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, not $array['index'];
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]";
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