Introduction to PHP Functions

Functions in PHP allow you to encapsulate a block of code that can be executed whenever needed. Functions help in reusability, maintainability, and organization of code.

1. Defining a Function

To define a function in PHP, use the function keyword followed by the function name, a pair of parentheses, and a block of code enclosed in curly braces.

<?php
function greet() {
    echo "Hello, World!";
}
?>

Explanation: The greet() function is defined to output "Hello, World!" when called. It does not accept any parameters and has no return value.

2. Calling a Function

After defining a function, you can call it by using its name followed by parentheses.

<?php
function greet() {
    echo "Hello, World!";
}

greet(); // Calls the function and outputs: Hello, World!
?>

Explanation: The greet() function is called, which executes the code inside the function and prints "Hello, World!" to the screen.

3. Function Parameters

Functions can accept parameters (or arguments) which are used to pass data to the function.

<?php
function greet($name) {
    echo "Hello, $name!";
}

greet("Alice"); // Outputs: Hello, Alice!
?>

Explanation: The greet($name) function takes a parameter $name and prints a greeting message using that name.

4. Returning Values

Functions can return values using the return statement. The returned value can be used in expressions or assigned to variables.

<?php
function add($a, $b) {
    return $a + $b;
}

$result = add(5, 3);
echo $result; // Outputs: 8
?>

Explanation: The add($a, $b) function takes two parameters, adds them together, and returns the result. The result is then printed.

5. Function with Default Parameters

Functions can have default parameter values. If no argument is passed for that parameter, the default value is used.

<?php
function greet($name = "Guest") {
    echo "Hello, $name!";
}

greet();       // Outputs: Hello, Guest!
greet("Alice"); // Outputs: Hello, Alice!
?>

Explanation: The greet($name) function has a default value of "Guest" for the $name parameter. If no value is provided, "Guest" is used by default.

6. Variable Scope

Variables in PHP have different scopes. A variable defined inside a function is local to that function and cannot be accessed outside of it. Global variables can be accessed inside functions using the global keyword.

<?php
$globalVar = "I am global";

function testScope() {
    global $globalVar;
    echo $globalVar; // Outputs: I am global
}

testScope();
?>

Explanation: The $globalVar variable is declared outside the function and is accessed inside the function testScope() using the global keyword.

7. Anonymous Functions

Anonymous functions, also known as closures, are functions that do not have a name. They can be assigned to variables and passed as arguments to other functions.

<?php
$square = function($n) {
    return $n * $n;
};

echo $square(4); // Outputs: 16
?>

Explanation: The anonymous function is assigned to the variable $square. It calculates the square of a number and is then called with the argument 4.