Introduction to PHP Variables

In PHP, variables are used to store data, such as numbers, strings, or arrays. A variable starts with the $ symbol, followed by the name of the variable.

Rules for Creating Variables in PHP

• A variable name must start with a letter or the underscore character (_).
• A variable name cannot start with a number.
• A variable name can only contain alphanumeric characters and underscores (A-z, 0-9, and _).
• Variable names are case-sensitive ($age and $AGE are different variables).

Examples of PHP Variables

<?php
$txt = "Hello, World!";
$number = 10;
$floatNumber = 10.5;
$isPHP = true;

echo $txt;           // Outputs: Hello, World!
echo $number;        // Outputs: 10
echo $floatNumber;   // Outputs: 10.5
echo $isPHP;         // Outputs: 1 (true is represented as 1)
?>

Explanation of the Example

In the above example:

• $txt is a string variable that stores the text "Hello, World!".
• $number is an integer variable that stores the value 10.
• $floatNumber is a float variable that stores the value 10.5.
• $isPHP is a boolean variable that stores the value true (which is represented as 1 when output).

PHP Data Types

PHP supports various data types that are used to store different kinds of data. The most common data types in PHP are:

• String
• Integer
• Float (Floating point numbers)
• Boolean
• Array
• Object
• NULL
• Resource

1. String

A string is a sequence of characters, like "Hello, World!".

<?php
$greeting = "Hello, World!";
echo $greeting; // Outputs: Hello, World!
?>

Explanation: In this example, $greeting is a string variable that stores the text "Hello, World!".

2. Integer

An integer is a non-decimal number between -2,147,483,648 and 2,147,483,647.

<?php
$number = 100;
echo $number; // Outputs: 100
?>

Explanation: Here, $number is an integer variable storing the value 100.

3. Float

A float (floating point number) is a number with a decimal point or a number in exponential form.

<?php
$price = 19.99;
echo $price; // Outputs: 19.99
?>

Explanation: In this example, $price is a float variable that stores the value 19.99.

4. Boolean

A Boolean represents two possible states: true or false.

<?php
$isLoggedIn = true;
echo $isLoggedIn; // Outputs: 1 (true is represented as 1)
?>

Explanation: Here, $isLoggedIn is a boolean variable that stores the value true.

5. Array

An array is a data structure that can hold multiple values.

<?php
$colors = array("Red", "Green", "Blue");
echo $colors[0]; // Outputs: Red
?>

Explanation: In this example, $colors is an array containing three values: "Red", "Green", and "Blue". The first value is accessed using the index 0.

6. Object

Objects are instances of classes. A class is a template for objects, and an object is created using the new keyword.

<?php
class Car {
    public $color;
    public function __construct($color) {
        $this->color = $color;
    }
    public function getColor() {
        return $this->color;
    }
}

$myCar = new Car("Blue");
echo $myCar->getColor(); // Outputs: Blue
?>

Explanation: In this example, Car is a class with a property $color and a method getColor(). An object $myCar is created from the class, and the color is set to "Blue".

7. NULL

The NULL data type represents a variable with no value.

<?php
$emptyVar = NULL;
var_dump($emptyVar); // Outputs: NULL
?>

Explanation: Here, $emptyVar is assigned the value NULL, meaning it has no value.

8. Resource

A resource is a special variable that holds a reference to an external resource, such as a database connection.

A resource is a special variable that holds a reference to an external resource, such as a database connection.

<?php
$file = fopen("test.txt", "r");
// $file is a resource representing the opened file
?>

Explanation: In this example, $file is a resource variable that holds the reference to the file test.txt opened in read mode.