First Steps: Syntax, Variables and Types

Why PHP?

PHP is a server-side language: the code runs on the server, which sends HTML (or JSON) back to the browser. It powers a very large part of the web, from WordPress to Laravel and Symfony. This course uses PHP 8.5, a modern, typed and fast version.

You can run a script in the terminal with php script.php, or through a web server. Let’s start with the terminal.

A first script

<?php
// Single-line comment
# Another single-line comment style
/* Comment
   on several lines */

echo "Hello world!\n"; // echo prints text; \n = line break

Two rules to remember: a PHP file starts with <?php, and every statement ends with a semicolon. In a file that contains only PHP, you don’t close the ?> tag at the end (this avoids sending stray whitespace).

Variables

A variable starts with $. You don’t declare its type: it is inferred from the value.

<?php
$prenom = "Inès";      // string
$age = 29;             // int (integer)
$taille = 1.68;        // float (decimal number)
$estAbonne = true;     // bool (true / false)
$parrain = null;       // null: no value

var_dump($age);        // int(29)
var_dump($taille);     // float(1.68)
echo gettype($prenom); // string

Names are case-sensitive: $age and $Age are two different variables. camelCase is generally used ($prixTotal).

For a value that must never change, you declare a constant: const TAUX_TVA = 0.2; (no $).

Strings

<?php
$prenom = "Inès";
$ville = 'Lyon';

// Concatenation with the dot
echo 'Hello ' . $prenom . '!' . "\n";

// Interpolation: only double quotes replace variables
echo "Hello $prenom, you live in $ville.\n";
echo 'Hello $prenom';            // prints literally: Hello $prenom

// Curly braces to remove ambiguity
$produit = "book";
echo "Two {$produit}s bought\n"; // Two books bought

// A few useful functions
echo strlen("PHP") . "\n";              // 3 (number of bytes)
echo mb_strlen("Inès") . "\n";          // 4 (number of characters, handles accents)
echo strtoupper("php") . "\n";          // PHP
echo number_format(1234.5, 2, ',', ' '); // 1 234,50

Careful: strlen counts bytes. With accented characters (UTF-8), use the mb_ functions such as mb_strlen.

Comparing: == or ===?

<?php
var_dump(5 == "5");   // bool(true)  : type conversion before comparison
var_dump(5 === "5");  // bool(false) : different types (int vs string)
var_dump(0 == "a");   // bool(false) since PHP 8

== converts types before comparing, which can be surprising. === checks the value and the type: it is the comparison to prefer.

Key takeaways

• <?php, semicolon, echo to print.
• Variables as $name, inferred types, var_dump() to inspect.
• Double quotes = interpolation; dot = concatenation.
• Use === by default.