PHP and MySQL Web Development 4th Ed-tqw-_darksiderg

Examining Variable Types
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Examining Variable Types
A variable’s type refers to the kind of data stored in it. PHP provides a set of data types.
Different data can be stored in different data types.
PHP’s Data Types
PHP supports the following basic data types:
n Integer—Used for whole numbers
n
n
n
n
Float (also called double)—Used for real numbers
String—Used for strings of characters
Boolean—Used for true or false values
Array—Used to store multiple data items (see Chapter 3,“Using Arrays”)
n Object—Used for storing instances of classes (see Chapter 6)
Two special types are also available: NULL and resource.Variables that have not been
given a value, have been unset, or have been given the specific value NULL are of type
NULL. Certain built-in functions (such as database functions) return variables that have
the type resource. They represent external resources (such as database connections).You
will almost certainly not directly manipulate a resource variable, but frequently they are
returned by functions and must be passed as parameters to other functions.
Type Strength
PHP is called weakly typed, or dynamically typed language. In most programming languages,
variables can hold only one type of data, and that type must be declared before
the variable can be used, as in C. In PHP, the type of a variable is determined by the
value assigned to it.
For example, when you created $totalqty and $totalamount, their initial types were
determined as follows:
$totalqty = 0;
$totalamount = 0.00;
Because you assigned 0, an integer, to $totalqty, this is now an integer type variable.
Similarly, $totalamount is now of type float.
Strangely enough, you could now add a line to your script as follows:
$totalamount = ‘Hello’;
The variable $totalamount would then be of type string. PHP changes the variable type
according to what is stored in it at any given time.