PHP Tutorial #2: Variables, Constants, and Data Types - Spider Cyber Team

PHP Tutorial #2: Variables and Data Types

Welcome back to the Spider Cyber Team backend series. Today, we will explore how PHP stores and manages data. Understanding how to use variables correctly is the first step toward building secure and powerful web applications.

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1. What are PHP Variables?

In PHP, a variable starts with the $ sign, followed by the name of the variable. Unlike many other languages, PHP is "Loosely Typed," meaning you don't have to declare the data type before using it.

Rules for PHP Variables:

• Must start with a letter or the underscore character _.
• Cannot start with a number.
• Are Case-Sensitive ($age and $AGE are two different variables).

<?php
    $txt = "Hello Spider Team!";
    $x = 5;
    $y = 10.5;

    echo $txt;
    echo "<br>";
    echo $x + $y; // Output: 15.5
?>

2. PHP Data Types

PHP supports several data types that allow you to handle different kinds of information:

• String: A sequence of characters (e.g., "Hello").
• Integer: Whole numbers (e.g., 100, -5).
• Float: Decimal numbers (e.g., 10.5).
• Boolean: Either true or false.
• Array: Stores multiple values in one single variable.
• Null: A variable that has no value assigned to it.

3. Constants in PHP

Constants are like variables, but once they are defined, they cannot be changed. They are global and can be used across the entire script. We use the define() function.

<?php
    // define(name, value)
    define("SITE_URL", "https://spider-team0.blogspot.com");

    echo SITE_URL; 
?>

4. Security Tip: Variable Sanitization

As a member of Spider Cyber Team, you should always remember: Never trust user input! When you store data from a user into a variable, you must sanitize it to prevent SQL Injection or XSS attacks. We will cover this in advanced lessons.

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Conclusion

Variables and Constants are the foundation of your backend logic. In the next lesson, we will learn about PHP Strings and Math functions to manipulate this data!

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