PHP Variables

Like most programming languages, PHP lets you create variables in your scripts. A variable is a storage container that holds a value. This value can change as the script runs. You can:

• Assign any value you like to a variable
• Access the value stored in a variable, and
• Change a variable’s value at any time.

Variables are useful because they let you write flexible scripts. For example, a script that can only add 3 and 4 together isn’t very useful. A script that can add any two values together, though, is much more flexible.

Creating a variable

To create a new variable in PHP, you can just write the variable’s name:

$myVariable;

Notice the dollar ($) symbol before the variable name. All PHP variables have a dollar symbol in front.

This is known as declaring a variable. It’s also a good idea to give the variable an initial value at the time you declare it — this is known as initializing the variable:

$myVariable = 23;

If you don’t initialize a new variable then it takes on a value of null.

Changing a variable’s value

You’ve just seen how to assign a value to a variable: you simply write the variable name, followed by an equals sign, followed by the value you want to assign.

To change a variable’s value, simply assign the new value:

$myVariable = 23;
$myVariable = 45;
$myVariable = "hello";

The first line of code creates a new variable with a numeric value of 23, while the second line changes the variable’s value to 45. The third line changes the value again — this time to a string of text, “hello”.PHP is a loosely-typed language, which means you can change the type of data that a variable holds whenever you like. In the above example, $myVariable starts off holding a number, and finishes by holding a string of text.

Using a variable’s value

To use the value of a variable in your script, simply write the variable’s name. For example, to display the value of $myVariable you’d use:

echo $myVariable;

To add the values of two variables $x and $y together and display the result, you could write:

echo $x + $y;

Variable names in PHP

Before leaving the topic of PHP variables, it’s worth taking a look at how to name variables. All PHP variable names have to follow these rules:

• They start with a $ (dollar) symbol.
• The first character after the dollar must be either a letter or a _ (underscore) symbol.
• The other characters may be letters, numbers, and/or underscores.

Variable names can be as long as you like, but it’s a good idea to keep them relatively short (otherwise they can get quite unwieldy). It’s also good to use meaningful variable names — for example, $numWidgets is much more useful than $nw.

PHP variable names are case-sensitive, which means that $myVariable and $MyVariable refer to different variables.

Now that you know how PHP variables work, you’re well on your way to writing useful PHP scripts!