Syntax Basics

beginner

Part of PHP Basics

Theory

This lesson covers the core PHP syntax you need to write functional scripts. PHP's syntax is similar to C and Perl, making it familiar to many developers.

Variables

PHP variables start with $ followed by the variable name. They are dynamically typed:

<?php
$name = "Alice";        // String
$age = 25;              // Integer
$price = 19.99;         // Float
$isActive = true;       // Boolean
$colors = ["red", "blue"]; // Array
$nothing = null;        // Null
?>

Naming rules:

Must start with a letter or underscore
Can contain letters, digits, and underscores
Case-sensitive ($name ≠ $Name)
Use snake_case by convention

Variable variables — using a variable's value as another variable's name:

<?php
$varName = "city";
$$varName = "New York";  // Creates $city = "New York"
echo $city;  // New York
?>

Data Types

PHP supports eight primitive data types:

<?php
// Scalar types
$string = "Hello";
$int = 42;
$float = 3.14;
$bool = true;
 
// Compound types
$array = [1, 2, 3];
$object = new stdClass();
$callable = function() { return "hi"; };
 
// Special types
$null = null;
?>

Type checking and conversion:

<?php
var_dump($value);     // Shows type and value
gettype($value);      // Returns type as string
is_string($value);    // Type checking functions
is_int($value);
is_array($value);
 
// Type casting
$int = (int) "42";           // 42
$float = (float) "3.14";     // 3.14
$string = (string) 100;      // "100"
$bool = (bool) "true";       // true
?>

echo vs print

Both output text, but with differences:

<?php
echo "Hello";                    // No return value
echo "Hello", " ", "World";      // Accepts multiple arguments
print "Hello";                   // Returns 1 (can use in expressions)
print "Hello World";             // Only one argument
 
// print_r and var_dump for debugging
$arr = [1, 2, 3];
print_r($arr);                   // Human-readable array
var_dump($arr);                  // With type information
?>

Strings

Single vs double quotes:

<?php
$name = "Alice";
 
// Single quotes — literal, no variable interpolation
echo 'Hello $name';     // Hello $name
 
// Double quotes — interpolates variables
echo "Hello $name";     // Hello Alice
 
// Curly braces for complex expressions
echo "Hello {$name}Smith";  // Hello AliceSmith
 
// Heredoc (multi-line with interpolation)
echo <<<EOT
Hello $name,
This is a multi-line
string.
EOT;
 
// Nowdoc (multi-line, no interpolation)
echo <<<'EOT'
This treats $name as literal.
EOT;
?>

Common string functions:

<?php
strlen("Hello");              // 5
strtoupper("hello");          // HELLO
strtolower("HELLO");          // hello
ucfirst("hello");             // Hello
ucwords("hello world");       // Hello World
trim("  hi  ");               // "hi"
str_replace("old", "new", $str);
substr("Hello World", 0, 5);  // Hello
strpos("Hello", "ll");        // 2
explode(",", "a,b,c");        // ["a", "b", "c"]
implode(", ", ["a", "b"]);    // "a, b"
?>

Constants

<?php
// define() — runtime constants
define("SITE_NAME", "My Website");
define("MAX_USERS", 100);
echo SITE_NAME;
 
// const — compile-time constants (in classes or top-level)
const VERSION = "1.0.0";
echo VERSION;
 
// Predefined constants
echo PHP_VERSION;
echo PHP_OS;
echo __LINE__;
echo __FILE__;
echo __DIR__;
?>

Operators

Arithmetic: +, -, *, /, %, ** (exponentiation)

Comparison: ==, === (identical), !=, !==, <, >, <=, >=, <=> (spaceship)

Logical: && (and), || (or), ! (not), and, or (lower precedence)

String: . (concatenation), .= (concatenating assignment)

Assignment: =, +=, -=, *=, /=, .=

<?php
// Loose vs strict comparison
var_dump(5 == "5");    // true (type coercion)
var_dump(5 === "5");   // false (different types)
 
// Spaceship operator (returns -1, 0, or 1)
echo 1 <=> 2;  // -1
echo 2 <=> 2;  // 0
echo 3 <=> 2;  // 1
 
// Null coalescing operator
$username = $_GET['user'] ?? 'guest';  // ?? provides default
 
// Ternary
$status = $age >= 18 ? "Adult" : "Minor";
?>

if/else and switch

<?php
$score = 85;
 
if ($score >= 90) {
    echo "A";
} elseif ($score >= 80) {
    echo "B";
} elseif ($score >= 70) {
    echo "C";
} else {
    echo "F";
}
 
// Alternative syntax (useful in templates)
if ($score >= 50): ?>
    <p>You passed!</p>
<?php endif; ?>
 
// Switch
$day = "Monday";
switch ($day) {
    case "Saturday":
    case "Sunday":
        echo "Weekend!";
        break;
    default:
        echo "Weekday";
        break;
}
?>

Loops

<?php
// for
for ($i = 0; $i < 5; $i++) {
    echo $i;
}
 
// while
$i = 0;
while ($i < 5) {
    echo $i++;
}
 
// do-while (always runs at least once)
$i = 0;
do {
    echo $i++;
} while ($i < 5);
 
// foreach (most common for arrays)
$fruits = ["Apple", "Banana", "Cherry"];
foreach ($fruits as $fruit) {
    echo $fruit;
}
 
// foreach with key
$ages = ["Alice" => 25, "Bob" => 30];
foreach ($ages as $name => $age) {
    echo "$name is $age";
}
 
// Alternative syntax (templates)
foreach ($items as $item): ?>
    <li><?= $item ?></li>
<?php endforeach; ?>
?>

Functions

<?php
// Basic function
function greet($name) {
    return "Hello, $name!";
}
echo greet("Alice");
 
// Default parameters
function multiply($a, $b = 1) {
    return $a * $b;
}
echo multiply(5);     // 5
echo multiply(5, 3);  // 15
 
// Type declarations
function add(int $a, int $b): int {
    return $a + $b;
}
 
// Strict types (declare at top of file)
declare(strict_types=1);
 
// Variable scope
$global = "outside";
function test() {
    global $global;  // Import global
    $local = "inside";
    echo $global;    // "outside"
    echo $local;     // "inside"
}
 
// Static variables (persist across calls)
function counter() {
    static $count = 0;
    return ++$count;
}
echo counter();  // 1
echo counter();  // 2
?>

Declare declare(strict_types=1); at the top of your PHP files to enforce strict type checking. This prevents automatic type coercion in function arguments and makes your code more predictable.

Practical Examples

Example 1: String Processing Functions

php

Example 2: Calculator with Functions

php

Use foreach instead of for when iterating over arrays. It's cleaner and less error-prone. Use the key => value syntax when you need the array keys.

Exercises

Data Type Explorer

easy

Create a PHP script that declares variables of different types (string, int, float, bool, null, array). Use var_dump() on each and display the type. Then demonstrate type juggling by performing operations between different types.

Expected Output:

Each variable displayed with var_dump showing its type and value, plus examples of implicit and explicit type conversion.

FizzBuzz with Loops

easy

Write a PHP script that prints numbers from 1 to 100. For multiples of 3, print 'Fizz' instead of the number. For multiples of 5, print 'Buzz'. For multiples of both, print 'FizzBuzz'.

Expected Output:

1, 2, Fizz, 4, Buzz, Fizz, 7, 8, Fizz, Buzz, 11, Fizz, 13, 14, FizzBuzz, ...

String Utility Library

medium

Create a set of string utility functions: truncate (crops at word boundary), slugify (URL-friendly), maskEmail (hides part of email), and contains (checks if string contains a substring).

Expected Output:

Hello...\nhello-world-php-is-great\nali***@example.com\nyes

Mini Quiz

Mini Project

Mini Project: Text Analysis Tool

Create a PHP web page that accepts a block of text, analyzes it, and displays statistics: character count, word count, sentence count, average word length, most common words, keyword density, and a readability score.

Requirements:

Bonus Challenge

Add a simple readability score using the Flesch-Kincaid formula. Generate a word cloud using HTML spans with varying font sizes based on frequency.