PHP Basics

PHP is a server-side scripting language designed for web development. This guide covers the fundamentals you need to get started with PHP programming.

Variables

PHP variables start with $ and are dynamically typed:

// Variable assignment
$name = "PHP";
$age = 30;
$price = 19.99;
$isActive = true;
$value = null;

// Variable naming
$user_name = "developer";  // snake_case
$userName = "developer";    // camelCase
$MAX_SIZE = 100;            // Constants (UPPERCASE)

// Variable variables
$var = "name";
$$var = "PHP";  // $name = "PHP"

// Variable scope
$global = "global";

function test() {
    global $global;  // Access global variable
    $local = "local";  // Local variable
}

Data Types

PHP has several data types:

// Scalar types
$string = "Hello, World!";
$integer = 42;
$float = 3.14;
$boolean = true;

// Compound types
$array = [1, 2, 3];
$object = new stdClass();

// Special types
$null = null;
$resource = fopen("file.txt", "r");

// Type checking
is_string($string);   // true
is_int($integer);     // true
is_array($array);     // true
is_null($null);       // true

// Type casting
$number = (int) "42";
$text = (string) 42;
$float = (float) "3.14";

Arrays

PHP arrays are ordered maps (can be arrays or dictionaries):

// Indexed arrays
$fruits = ["apple", "banana", "orange"];
$numbers = array(1, 2, 3, 4, 5);

// Accessing elements
$fruits[0]        // "apple"
$fruits[1]       // "banana"
$fruits[-1]      // "orange" (PHP 7.1+)

// Adding elements
$fruits[] = "grape";        // Add to end
array_push($fruits, "mango"); // Add to end
array_unshift($fruits, "kiwi"); // Add to beginning

// Removing elements
array_pop($fruits);         // Remove last
array_shift($fruits);       // Remove first
unset($fruits[1]);          // Remove at index

// Associative arrays
$person = [
    "name" => "John",
    "age" => 30,
    "city" => "New York"
];

// Accessing associative array
$person["name"]   // "John"
$person["age"]    // 30

// Array functions
count($fruits);              // Get length
in_array("apple", $fruits);  // Check if contains
array_search("banana", $fruits); // Find index
array_merge($fruits, ["grape"]); // Merge arrays
array_keys($person);        // Get keys
array_values($person);      // Get values

Loops

PHP offers several iteration methods:

// For loop
for ($i = 0; $i < 5; $i++) {
    echo $i;
}

// Foreach loop (most common for arrays)
$fruits = ["apple", "banana", "orange"];
foreach ($fruits as $fruit) {
    echo $fruit;
}

// Foreach with keys
foreach ($fruits as $index => $fruit) {
    echo "$index: $fruit";
}

// Foreach with associative arrays
$person = ["name" => "John", "age" => 30];
foreach ($person as $key => $value) {
    echo "$key: $value";
}

// While loop
$count = 0;
while ($count < 5) {
    echo $count;
    $count++;
}

// Do-while loop
do {
    echo $count;
    $count--;
} while ($count > 0);

// Loop control
foreach ($fruits as $fruit) {
    if ($fruit === "banana") {
        continue;  // Skip to next iteration
    }
    if ($fruit === "orange") {
        break;  // Exit loop
    }
    echo $fruit;
}

Conditionals

Control flow with if/else statements:

// If/else
$age = 20;
if ($age >= 18) {
    echo "Adult";
} elseif ($age >= 13) {
    echo "Teenager";
} else {
    echo "Child";
}

// Ternary operator
$status = $age >= 18 ? "Adult" : "Minor";

// Null coalescing operator (PHP 7+)
$name = $username ?? "Guest";

// Null coalescing assignment (PHP 7.4+)
$data ??= "default";

// Logical operators
if ($age >= 18 && $hasLicense) {
    echo "Can drive";
}

if ($isWeekend || $isHoliday) {
    echo "Day off";
}

if (!$isComplete) {
    echo "Not done yet";
}

// Switch statement
$grade = "B";
switch ($grade) {
    case "A":
        echo "Excellent";
        break;
    case "B":
        echo "Good";
        break;
    case "C":
        echo "Average";
        break;
    default:
        echo "Needs improvement";
}

Functions

Functions are defined with function:

// Simple function
function greet($name) {
    return "Hello, $name!";
}

echo greet("PHP");  // "Hello, PHP!"

// Function with default parameters
function greet($name = "World") {
    return "Hello, $name!";
}

// Function with type hints (PHP 7+)
function add(int $x, int $y): int {
    return $x + $y;
}

// Function returning multiple values (array)
function get_name_and_age() {
    return ["John", 30];
}

list($name, $age) = get_name_and_age();
// Or (PHP 7.1+)
[$name, $age] = get_name_and_age();

// Variable functions
$func = "greet";
echo $func("PHP");  // Calls greet()

// Anonymous functions (closures)
$greet = function($name) {
    return "Hello, $name!";
};

echo $greet("PHP");

// Arrow functions (PHP 7.4+)
$add = fn($x, $y) => $x + $y;
echo $add(5, 3);  // 8

Classes

PHP supports object-oriented programming:

// Class definition
class Person {
    // Properties
    public $name;
    private $age;
    protected $email;
    
    // Constructor
    public function __construct($name, $age) {
        $this->name = $name;
        $this->age = $age;
    }
    
    // Getter method
    public function getAge() {
        return $this->age;
    }
    
    // Setter method
    public function setAge($age) {
        $this->age = $age;
    }
    
    // Instance method
    public function introduce() {
        return "Hi, I'm {$this->name} and I'm {$this->age} years old";
    }
    
    // Static method
    public static function create($name, $age) {
        return new self($name, $age);
    }
}

// Creating objects
$person = new Person("John", 30);
echo $person->introduce();
$person->setAge(31);

// Static method call
$person2 = Person::create("Jane", 25);

Inheritance

PHP supports class inheritance:

// Parent class
class Animal {
    protected $name;
    
    public function __construct($name) {
        $this->name = $name;
    }
    
    public function makeSound() {
        echo "Some sound";
    }
}

// Child class
class Dog extends Animal {
    public function makeSound() {
        echo "Woof!";
    }
    
    public function wagTail() {
        echo "{$this->name} is wagging tail";
    }
}

// Using inheritance
$dog = new Dog("Buddy");
$dog->makeSound();  // "Woof!"
$dog->wagTail();    // "Buddy is wagging tail"

String Functions

PHP has many built-in string functions:

$text = "Hello, World!";

// String manipulation
strlen($text);              // Get length
strtoupper($text);          // "HELLO, WORLD!"
strtolower($text);          // "hello, world!"
ucfirst($text);             // "Hello, world!"
ucwords($text);             // "Hello, World!"

// String searching
strpos($text, "World");     // 7 (position)
str_contains($text, "World"); // true (PHP 8+)
str_replace("World", "PHP", $text); // "Hello, PHP!"

// String extraction
substr($text, 0, 5);        // "Hello"
substr($text, 7);           // "World!"

// String splitting
explode(", ", $text);       // ["Hello", "World!"]
implode(" - ", ["Hello", "World"]); // "Hello - World"

// String formatting
sprintf("Hello, %s!", "PHP"); // "Hello, PHP!"
printf("Hello, %s!", "PHP");  // Prints directly