Page 73 - Beginning PHP 5.3

Chapter 3: PHP Language Basics
Many programming languages prevent you from using a variable without first explicitly declaring
(creating) it. But PHP lets you use variables at any point just by naming them. This is not always the
blessing you might think; if you happen to use a nonexistent variable name by mistake, no error message
is generated, and you may end up with a hard - to - find bug. In most cases, though, it works just fine and
is a helpful feature.

When you declare a variable in PHP, it ’ s good practice to assign a value to it at the same time. This is
known as initializing a variable. By doing this, anyone reading your code knows exactly what value the
variable holds at the time it ’ s created. (If you don ’ t initialize a variable in PHP, it ’ s given the default
value of null .)

Here ’ s an example of declaring and initializing a variable:

$my_first_variable = 3;

This creates the variable called $my_first_variable , and uses the = operator to assign it a value of 3.
(You look at = and other operators later in this chapter.)

Looking back at the addition example earlier, the following script creates two variables, initializes them
with the values 5 and 6 , then outputs their sum ( 11 ):

$x = 5;
$y = 6;
echo $x + $y;

Understanding Data Types

All data stored in PHP variables fall into one of eight basic categories, known as data types . A variable ’ s
data type determines what operations can be carried out on the variable ’ s data, as well as the amount of
memory needed to hold the data.

PHP supports four scalar data types. Scalar data means data that contains only a single value. Here ’ s a
list of them, including examples:

Scalar Data Type Description Example

Integer A whole number 15
Float A floating - point number 8.23

String A series of characters “Hello, world!”
Boolean Represents either true or false true

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