Imagine you are building a shopping website.

You need to store:

• Customer Name
• Email
• Product Price
• Total Quantity
• Login Status
• Order Number

How does PHP remember all of this information?

It uses Variables.

Sometimes we also need information that never changes.

For example:

• Website Name
• Company Name
• VAT Rate
• PI Value

PHP stores those using Constants.

Finally, PHP needs to understand what kind of information it is storing.

For example:

John

is text.

100

is a number.

true

is a Boolean value.

These are called Data Types.

By the end of this lesson you will understand all three.

What is a Variable?

A variable is a named container used to store data.

Think of it as a labelled box.

Example:

Name Box
------------
Ibrahim

Whenever you need the name, you simply open the box.

Instead of writing

Ibrahim

100 times, you store it once inside a variable.

Real Life Example

Imagine your room.

You have boxes labelled:

Books

Clothes

Laptop

Documents

Each box stores different things.

PHP variables work exactly the same way.

Example:

$name

$email

$price

$total

Each variable stores different information.

Variable Syntax

PHP variables always begin with

$

Example

$name = "Ibrahim";

Let’s understand this.

$name

Variable name.

=

Assignment operator.

"Ibrahim"

The value.

;

End of statement.

Your First Variable

<?php

$name = "Ibrahim";

echo $name;

?>

Output

Ibrahim

Explanation

Step 1

PHP creates a variable called

$name

Step 2

It stores

Ibrahim

inside it.

Step 3

When

echo $name;

runs,

PHP prints the stored value.

Variables Can Store Different Data

Text

$name = "Ibrahim";

Number

$age = 30;

Decimal

$price = 49.99;

True/False

$isLoggedIn = true;

Array

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

Variable Naming Rules

Good examples

$userName

$productPrice

$totalAmount

$studentAge

Bad examples

$1name

$user-name

$total amount

Rules

A variable:

• Starts with $
• Must begin with a letter or underscore after $
• Cannot begin with a number
• Cannot contain spaces
• Cannot contain hyphens
• Is case-sensitive

Variables are Case Sensitive

$name = "Ibrahim";

echo $name;

works.

But

echo $Name;

is different.

PHP sees

$name

and

$Name

as different variables.

Always use one naming style consistently, such as camelCase.

Declaring Multiple Variables

$name = "Ibrahim";

$age = 28;

$country = "Germany";

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

Output

Ibrahim

28

Germany

Updating Variables

Variables can change.

$score = 10;

echo $score;

$score = 20;

echo $score;

Output

10

20

PHP replaced the old value with the new one.

Variable Variables

PHP even allows variables whose names are stored in another variable.

$name = "language";

$language = "PHP";

echo $$name;

Output

PHP

This feature exists but is rarely needed.

What is a Constant?

A constant is a value that cannot change after it is created.

Example

Website Name

IbrahimX Academy

This rarely changes.

Instead of using a variable, use a constant.

Creating Constants

PHP provides

define()

Example

define("SITE_NAME", "IbrahimX Academy");

echo SITE_NAME;

Output

IbrahimX Academy

Notice there is no dollar sign.

Constants vs Variables

Variable

$name = "Ibrahim";

Can change.

Constant

define("SITE_NAME", "IbrahimX");

Cannot change.

Why Use Constants?

Perfect for

• Website Name
• Database Version
• VAT Rate
• API Version
• Company Name
• Maximum Upload Size

What are Data Types?

Data Type tells PHP what kind of information is being stored.

PHP supports several data types.

String

Stores text.

$name = "Ibrahim";

Output

Ibrahim

Integer

Whole numbers.

$age = 28;

Examples

1

50

100

1000

Float

Decimal numbers.

$price = 299.95;

Examples

5.5

10.75

999.99

Boolean

Only two values.

true

false

Example

$isAdmin = true;

Useful for

• Login
• Success
• Error
• Permissions

Array

Stores multiple values.

$colors = [

"Red",

"Blue",

"Green"

];

Arrays are covered in detail later.

NULL

Means no value.

$name = null;

Object

Objects are created from Classes.

$user = new User();

Objects are covered in the OOP section.

Resource

Special data created by PHP.

Example

Database connections.

Checking Data Types

PHP provides

var_dump()

Example

$name = "Ibrahim";

var_dump($name);

Output

string(8) "Ibrahim"

Another example

$age = 28;

var_dump($age);

Output

int(28)

Checking Type Only

gettype()

Example

$price = 99.95;

echo gettype($price);

Output

double

Type Casting

Convert one type into another.

Example

$price = "100";

$number = (int)$price;

echo $number;

Output

100

---

Interview Questions

Coding Problems

Problem 1

Create a variable called

$name

Store your name and print it.

Solution

$name = "Ibrahim";

echo $name;

Problem 2

Store your age.

Print

My age is 28

Solution

$age = 28;

echo "My age is " . $age;

Problem 3

Create a constant called

COMPANY

Solution

define("COMPANY","IbrahimX");

echo COMPANY;

Problem 4

Create variables

Product

Price

Quantity

Display

Laptop

800

2

Problem 5

Find the data type.

$price = 50.25;

Solution

var_dump($price);

Output

float(50.25)

Mini Project

Student Information Card

Create

$name

$age

$country

$course

$email

Display them inside an HTML card.

This project teaches:

• Variables
• Strings
• Integers
• Output
• PHP inside HTML

Best Practices

• Use meaningful variable names like $productPrice instead of $x.
• Keep variable names consistent using camelCase.
• Use constants for values that never change.
• Avoid unnecessary global variables.
• Check data types with var_dump() during debugging.
• Use descriptive names that make your code self-explanatory.

Common Mistakes

• Forgetting the $ before a variable name.
• Using spaces or hyphens in variable names.
• Mixing uppercase and lowercase variable names ($name vs $Name).
• Trying to change a constant after defining it.
• Storing the wrong type of data without understanding type conversion.