SEO Title: PHP Variables, Constants, and Data Types Explained for Beginners

Meta Description: Learn PHP variables, constants, and data types with practical examples. A beginner-friendly guide to mastering PHP fundamentals.

PHP Variables, Constants, and Data Types Explained

In the previous article, we learned what PHP is and how it works. In this tutorial, we’ll explore three fundamental concepts every PHP developer must understand:

• Variables
• Constants
• Data Types

These concepts form the foundation of PHP programming and are used in every PHP application, including WordPress and Laravel projects.

What is a Variable in PHP?

A variable is used to store data that can be used and modified throughout your program.

In PHP, variables start with a dollar sign ($).

Syntax

$variable_name = value;

Example

<?php

$name = "Loki";
$age = 25;

echo $name;
echo "<br>";
echo $age;

?>

Output

Loki
25

Rules for Naming Variables

Valid Variable Names

$name = "John";
$user_age = 25;
$_city = "Surat";

Invalid Variable Names

$1name = "John";
$user-age = 25;

Rules

• Must start with $
• Must begin with a letter or underscore
• Cannot start with a number
• Cannot contain spaces
• Variable names are case-sensitive

Example:

$name = "Loki";
$Name = "Ali";

echo $name;
echo $Name;

These are treated as different variables.

Assigning Values to Variables

String

$name = "Loki";

Integer

$age = 25;

Float

$price = 99.99;

Boolean

$isLoggedIn = true;

Displaying Variables

Using echo:

$name = "Loki";

echo $name;

Output:

Loki

Combining Variables with Text

Method 1: Concatenation

$name = "Loki";

echo "My name is " . $name;

Output:

My name is Loki

Method 2: Double Quotes

$name = "Loki";

echo "My name is $name";

Output:

My name is Loki

What is a Constant in PHP?

A constant is a value that cannot be changed after it has been defined.

Unlike variables, constants do not use the $ symbol.

Syntax

define("SITE_NAME", "My Website");

Example

<?php

define("SITE_NAME", "Loki Blog");

echo SITE_NAME;

?>

Output:

Loki Blog

Why Use Constants?

Constants are useful for values that never change.

Examples:

• Website name
• Database configuration
• API URLs
• Company information

define("COMPANY_NAME", "ABC Solutions");
define("SUPPORT_EMAIL", "support@example.com");

PHP Data Types

A data type defines what kind of value a variable can store.

PHP supports several data types.

1. String

A string is a sequence of characters.

$name = "Loki";

Example:

echo $name;

Output:

Loki

2. Integer

Integers are whole numbers.

$age = 25;

Examples:

$count = 100;
$year = 2026;

3. Float (Double)

Floats contain decimal values.

$price = 99.99;

Example:

$rating = 4.5;

4. Boolean

A Boolean can only have two values:

true
false

Example:

$isAdmin = true;
$isPaid = false;

5. Array

Arrays store multiple values in a single variable.

Example:

$colors = ["Red", "Green", "Blue"];

Accessing an array item:

echo $colors[0];

Output:

Red

6. NULL

NULL means the variable has no value.

Example:

$name = null;

Checking Data Types

PHP provides the var_dump() function.

Example:

$name = "Loki";

var_dump($name);

Output:

string(4) "Loki"

Another example:

$age = 25;

var_dump($age);

Output:

int(25)

Real-World Example

Imagine you’re creating a user profile.

<?php

$name = "Loki";
$age = 25;
$isPremium = true;

define("SITE_NAME", "Loki Tutorials");

echo "Welcome to " . SITE_NAME;
echo "<br>";
echo "Name: " . $name;
echo "<br>";
echo "Age: " . $age;

?>

Output:

Welcome to Loki Tutorials
Name: Loki
Age: 25

Common Beginner Mistakes

Forgetting the Dollar Sign

Wrong:

name = "Loki";

Correct:

$name = "Loki";

Using Quotes Around Constants

Wrong:

echo "SITE_NAME";

Correct:

echo SITE_NAME;

Variable Case Sensitivity

$name = "Loki";
$Name = "Ali";

These are different variables.