PHP Keywords

Keyword Categories

🔹 Control Flow Keywords

Control flow keywords determine which code blocks execute based on conditions. They are fundamental to creating dynamic, decision-making programs.

<?php
$age = 18;

// if, else, elseif
if ($age < 13) {
    echo "Child";
} elseif ($age < 18) {
    echo "Teenager";
} else {
    echo "Adult";
}

echo "\n\n";

// switch, case, default
$day = "Monday";
switch ($day) {
    case "Monday":
        echo "Start of week";
        break;
    case "Friday":
        echo "End of week";
        break;
    default:
        echo "Midweek";
}
?>

🔹 Loop Keywords

Loop keywords allow you to repeat code multiple times. Each loop type serves different purposes, from counting iterations to processing arrays.

<?php
// for loop
for ($i = 1; $i <= 3; $i++) {
    echo "Count: $i\n";
}

echo "\n";

// while loop
$x = 1;
while ($x <= 3) {
    echo "While: $x\n";
    $x++;
}

echo "\n";

// foreach loop
$colors = ["red", "green", "blue"];
foreach ($colors as $color) {
    echo "Color: $color\n";
}
?>

🔹 Function Keywords

Function keywords help you create reusable code blocks. The return keyword sends values back from functions, while function defines them.

<?php
// function and return
function greet($name) {
    return "Hello, " . $name . "!";
}

echo greet("Alice");

echo "\n\n";

// Function with multiple returns
function checkAge($age) {
    if ($age >= 18) {
        return "Adult";
    }
    return "Minor";
}

echo checkAge(25);
echo "\n";
echo checkAge(15);
?>

🔹 Class and Object Keywords

Object-oriented programming keywords define classes, create objects, and manage inheritance. These are essential for building structured, reusable code.

<?php
// class, new, public, private
class Car {
    public $brand;
    private $speed = 0;
    
    public function __construct($brand) {
        $this->brand = $brand;
    }
    
    public function accelerate() {
        $this->speed += 10;
        return $this->speed;
    }
}

$myCar = new Car("Toyota");
echo "Brand: " . $myCar->brand . "\n";
echo "Speed: " . $myCar->accelerate() . " km/h";
?>

🔹 Break and Continue Keywords

Break exits a loop immediately, while continue skips the current iteration and moves to the next. These control loop execution flow precisely.

<?php
// break - exit loop
for ($i = 1; $i <= 5; $i++) {
    if ($i == 3) {
        break;  // Stop at 3
    }
    echo "Break: $i\n";
}

echo "\n";

// continue - skip iteration
for ($i = 1; $i <= 5; $i++) {
    if ($i == 3) {
        continue;  // Skip 3
    }
    echo "Continue: $i\n";
}
?>

🔹 Include and Require Keywords

These keywords insert code from other files into your script. Require stops execution if the file is missing, while include continues with a warning.

<?php
// include - continues on error
include 'header.php';

// require - stops on error
require 'config.php';

// include_once - includes only once
include_once 'functions.php';

// require_once - requires only once
require_once 'database.php';

echo "All files loaded!";
?>

🔹 Try, Catch, Finally Keywords

Exception handling keywords manage errors gracefully. Try contains risky code, catch handles errors, and finally runs cleanup code regardless of errors.

<?php
function divide($a, $b) {
    if ($b == 0) {
        throw new Exception("Cannot divide by zero!");
    }
    return $a / $b;
}

try {
    echo "Result: " . divide(10, 2) . "\n";
    echo "Result: " . divide(10, 0) . "\n";
} catch (Exception $e) {
    echo "Error: " . $e->getMessage() . "\n";
} finally {
    echo "Calculation complete.";
}
?>

🔹 Common PHP Keywords List