What are PHP variables ? PHP Tutorial – Chapter 3

 

In this tutorial, you’ll learn about PHP Variables, Constants and Parameters.

Regular Variables

Variables are containers which we use for storing information. PHP variables work a bit differently to other languages so I suggest you pay close attention here.

A variable starts with a dollar sign ($) which is then followed by the name of the variable. That is then followed by a = sign and the value is entered after that. After the value you need a semi-colon as usual. Let’s have an example.

PHP Code:

<?php

$variable_name = 100;

?>

There are some important things you must remember when setting a variable name:

• The name of a variable must start with a letter or an underscore.
• Variable names are case sensitive (so $people would not be the same as $PEOPLE).
• A variable name cannot start with a number.
• A variable name can contain only letters, numbers and underscores.

When defining a variable you do not have to tell PHP the data type. This is where it is a bit different to other languages and shares more in common with something like python as PHP looks at what you set the variable too and gives it a datatype based on that.

Because of this, you also never need to declare a variable, it is created the moment you assign a value to it.

You can also use variables in other functions or constructs instead of directly typing in data. This comes in handy when you will be using a value more than once and don’t want to have to retype it and/or when the value of it will be changing often. For example:

PHP Code:

<?php

$name = “AceDommete”;

//Since I put in the quotation marks PHP knows that is a string.

echo $name;

//Now the echo construct goes and looks for variable $name and outputs it.

?>

Constants

A constant is similar to a variable except it is defined once then cannot be undefined or have its value changed. The same rules for making a constant variable name apply here.

To create a constant you use the define() function.

PHP Code:

define(name, value, case-insensitive)

Parameters:

• name: Specifies the name of the constant.
• value: Specifies the value of the constant.
• case-insensitive: Should the constant name be case sensitive? This is defaulted to false.

Example:

PHP Code:

<?php

define(“HELLO”, “Hello there friend.”);

echo HELLO;

//Outputs “Hello there friend.”

?>

Example using case sensitive:

PHP Code:

<?php

define(“HELLO”, “Hello my friend.”, true);

echo hello;

//Outputs “Hello my friend.”

?>

You can also define constants by using the const variable. This works in exactly the same way but is always case-sensitive and is defined a little differently.

PHP Code:

<?php

const CONSTANT = value;

?>

Instead of using define, you simple remove the $ from in front of a variable and use the keyword const in front of the variable name.