PHP Lesson 2

PHP Lesson 2: Variables and Data Types (The Building Blocks)

Welcome back! In Lesson 1, you learned how to display simple text using echo. Now, we're going to learn how to store, manipulate, and reuse information using Variables.

📦 Understanding Variables

A variable is essentially a container or a named memory location used to store data. Think of it like a label on a box: the label is the variable name, and whatever is inside the box is the value.

In PHP, a few key rules apply to variables:

1. Starts with $: All variable names must begin with a dollar sign ($).

2. Assignment: We use the equals sign (=) to assign a value to a variable.

3. Naming Rules: Variable names must start with a letter or an underscore (_) and can only contain alphanumeric characters and underscores (A-z, 0-9, and _). They are case-sensitive (e.g., $name is different from $Name).

Basic Variable Declaration

Here is how you declare a variable and then use the echo statement to display its value:

PHP

<?php
    // 1. Declare a variable named $username and assign it a string value
    $username = "CodeMaster78"; 

    // 2. Declare a variable named $age and assign it a number value
    $age = 25;

    // 3. Use echo to output the value stored in the variable
    echo "Welcome, " . $username . "! You are " . $age . " years old.";
?>

Output: Welcome, CodeMaster78! You are 25 years old.

💡 The Dot (.) Operator: In PHP, the dot operator is used to concatenate (join) strings and variables together.

📊 PHP Data Types

A Data Type defines the kind of data a variable can hold (e.g., a number, text, a true/false value). PHP is a loosely typed language, meaning you don't have to explicitly tell PHP what data type a variable will be—it figures it out automatically!

Here are the most common data types you'll use:

Data Type	Description	Example
String	A sequence of characters (text).	$name = "Alice";
Integer	A whole number (positive or negative).	$count = 42;
Float	A number with a decimal point.	$price = 19.99;
Boolean	A value that is either TRUE or FALSE.	$isLoggedIn = true;
Array	Stores multiple values in a single variable. (Next lesson!)	$colors = ["Red", "Blue"];

Working with Different Types

PHP

<?php
    // --- String ---
    $greeting = "Hello, beginner!";
    echo $greeting . "<br>";

    // --- Integer ---
    $num1 = 10;
    $num2 = 5;
    $sum = $num1 + $num2; // Simple arithmetic!
    echo "10 + 5 = " . $sum . "<br>"; 

    // --- Float ---
    $taxRate = 0.05;
    $totalPrice = 100 * (1 + $taxRate);
    echo "Total price: $" . $totalPrice . "<br>";

    // --- Boolean ---
    $isAvailable = false;
    // Booleans are usually used in decision-making structures (if/else)
    if ($isAvailable == true) {
        echo "Item is in stock!";
    } else {
        echo "Item is currently unavailable.";
    }
?>

🧠 Important PHP Concepts

Dynamic Typing

If you assign a new value of a different type to an existing variable, PHP automatically changes the variable's type.

PHP

<?php
    $data = 100;         // $data is an Integer
    echo $data . "<br>";

    $data = "one hundred"; // Now, $data is a String
    echo $data . "<br>"; 
?>

String Interpolation (A Neat Shortcut!)

When using double quotes ("), you can directly embed the variable name inside the string, and PHP will automatically replace it with its value. This is called interpolation.

PHP

<?php
    $product = "Widget X";
    $cost = 50;

    // With concatenation (dot operator):
    echo "The item is " . $product . " and it costs $" . $cost . "<br>";
    
    // With interpolation (simpler and cleaner!):
    echo "The item is $product and it costs $$cost"; // Note: The second $ is just for the currency symbol.
?>

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🚀 Your Second Challenge!

Create a PHP script that calculates a simple discount.

1. Declare a variable $originalPrice and set it to a float value (e.g., 59.99).

2. Declare a variable $discountPercentage and set it to a whole number (e.g., 10).

3. Calculate the final price (Hint: Original Price * (1 - Discount/100)).

4. Use echo and string interpolation to display the result in a readable sentence (e.g., "The final price after a 10% discount is $53.99").

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You now know how to store information! Next, we will cover Arrays, which allow you to store collections of related data efficiently.