PHP — Syntax

Q: What is Syntax in PHP?

Syntax is a fundamental concept in PHP. This lesson explains it step by step with clear examples, making it easy for beginners to understand.

Q: How do I learn Syntax?

Start by reading the explanation above, then try the code examples. Practice by modifying the examples and experimenting with different values. Hands-on practice is the best way to learn Syntax.

Q: Why is Syntax important in PHP?

Syntax is essential for PHP development. Understanding this concept will help you write better code and solve real-world problems more effectively.

PHP tags

PHP code lives between <?php and ?>:

<?php
// PHP code here
echo "Hello";
?>

In pure PHP files, omit the closing tag:

<?php
// No closing tag needed — this is preferred
echo "Hello";

Statements end with semicolons

<?php
$x = 5;
echo "Hello\n";
$y = $x + 1;
?>

Every complete instruction ends with a semicolon. Missing semicolons cause parse errors.

Embedding PHP in HTML

PHP was designed to mix with HTML:

<?php
$name = "Ada";
$age = 36;
?>
<!DOCTYPE html>
<html>
<body>
    <h1>Hello, <?php echo $name; ?>!</h1>
    <p>You are <?php echo $age; ?> years old.</p>
</body>
</html>

The <?php ... ?> tags switch between HTML and PHP. The server executes the PHP and sends the result to the browser.

Short echo tags

<?php
$name = "Ada";
?>
<p>Hello, <?= $name ?>!</p>

<?= $name ?> is shorthand for <?php echo $name ?>. It's always available and widely used.

Variables

PHP variables start with $:

<?php
$age = 25;          // integer
$name = "Ada";      // string
$pi = 3.14;         // float
$active = true;     // boolean
$items = [1, 2, 3]; // array
$data = null;       // null
?>

Variable names are case-sensitive: $name ≠ $Name.

Naming rules

<?php
$student_name = "Ada";     // good: snake_case
$studentName = "Ada";      // legal, but PHP convention is snake_case
$2cool = "x";              // ERROR: can't start with a digit
$my-name = "x";            // ERROR: dash means subtraction
?>

PHP convention uses snake_case for variables and functions, PascalCase for classes.

Comments

<?php
// Single-line comment

# Also a single-line comment

/*
   Multi-line comment
   spans several lines
*/

echo "Code runs";
?>

Blocks

Use curly braces to group statements:

<?php
if ($age >= 18) {
    echo "Adult";
    echo "Can vote";
}
?>

Semicolons in arrays

<?php
$fruits = [
    "apple",
    "banana",
    "cherry",  // trailing comma is fine
];

$person = [
    "name" => "Ada",
    "age" => 36,  // trailing comma is fine
];
?>

Trailing commas are allowed and encouraged — they make diffs cleaner.

Strict vs loose comparison

<?php
// Loose comparison (==) — type coercion
echo 10 == "10";    // true
echo 0 == "";       // true
echo null == false;  // true

// Strict comparison (===) — no coercion
echo 10 === "10";   // false (different types)
echo 0 === "";      // false (different types)
echo null === false; // false (different types)
?>

Always use === and !== to avoid unexpected type coercion.

Error handling

<?php
// Display errors (development only)
ini_set('display_errors', 1);
error_reporting(E_ALL);

// Try-catch
try {
    throw new Exception("Something went wrong");
} catch (Exception $e) {
    echo "Error: " . $e->getMessage();
}
?>

Include files

<?php
// Include a file (warning on failure)
include 'config.php';

// Require a file (fatal error on failure)
require 'database.php';

// Include once
include_once 'helpers.php';

// Require once
require_once 'config.php';
?>

Use require for files your script can't run without. Use include for optional files.

Constants

<?php
// Define a constant
define('APP_NAME', 'Codenatomy');
define('MAX_USERS', 1000);

echo APP_NAME;   // Codenatomy
echo MAX_USERS;  // 1000

// Can't reassign
// APP_NAME = "New"; // ERROR
?>

Constants don't use $ and can't be changed after definition.

Mini Practice

Create a PHP file that embeds variables in HTML output
Use the short echo tag <?= to output a variable
Compare == and === with different types — observe the differences
Create an array of five items and print each one
Define three constants and use them in a formatted string

Next: variables and data types →

Frequently Asked Questions about Syntax

What is Syntax in PHP?