functions.md

🧰 Functions in PHP

Unlock reusable code - Functions organize logic, manage data, and streamline your PHP projects!

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🌟 What Are Functions?

Functions are reusable blocks of code that perform specific tasks. They can take inputs (parameters), process them, and return outputs. PHP offers built-in functions and lets you create custom ones!

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🛠️ Function Basics

Defining a Function

Use the function keyword, a name, and optional parameters.

function greet($name) {
    echo "Hello, $name!";
}
greet("User"); // Outputs: Hello, User!

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1. Returning Data from Functions

Return a value using the return statement.

function add($a, $b) {
    return $a + $b;
}
$result = add(5, 3);
echo $result; // Outputs: 8

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2. Returning Arrays

Return multiple values as an array.

function getStats() {
    return ["score" => 95, "level" => 3];
}
$stats = getStats();
echo $stats["score"]; // Outputs: 95

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3. Returning Lists

Use list() to unpack array returns (older style).

function getCoordinates() {
    return [10, 20];
}
list($x, $y) = getCoordinates();
echo "X: $x, Y: $y"; // Outputs: X: 10, Y: 20

Note: Modern PHP favors array destructuring: [$x, $y] = getCoordinates();

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4. Returning References

Return a variable by reference with &.

function &getValue() {
    static $value = 42;
    return $value;
}
$ref = &getValue();
$ref = 100;
echo getValue(); // Outputs: 100

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5. Introducing Variable Scope in PHP

Variables have scope—local by default.

$globalVar = "Outside";
function testScope() {
    $localVar = "Inside";
    echo $localVar; // Outputs: Inside
}
testScope();
echo $globalVar; // Outputs: Outside
// echo $localVar; // Error: Undefined

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6. Accessing Global Data

Use global or the $GLOBALS array.

$count = 5;
function increment() {
    global $count;
    $count++;
}
increment();
echo $count; // Outputs: 6

With $GLOBALS:

$count = 5;
function incrementGlobals() {
    $GLOBALS["count"]++;
}
incrementGlobals();
echo $count; // Outputs: 6

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7. Working with Static Variables

Retain values between calls with static.

function counter() {
    static $num = 0;
    $num++;
    return $num;
}
echo counter(); // Outputs: 1
echo counter(); // Outputs: 2

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8. PHP Conditional Functions

Functions with conditional logic.

function checkAge($age) {
    if ($age >= 18) {
        return "Adult";
    }
    return "Minor";
}
echo checkAge(20); // Outputs: Adult

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9. PHP Variable Functions

Call functions dynamically by name.

function sayHello() {
    echo "Hello!";
}
$funcName = "sayHello";
$funcName(); // Outputs: Hello!

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10. Nesting Functions

Define functions inside others (rarely used).

function outer() {
    function inner() {
        echo "Nested!";
    }
    inner();
}
outer(); // Outputs: Nested!

Caution: Inner functions become global after outer() runs once.

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11. Creating Include Files

Move functions to separate files.

helpers.php:

function multiply($a, $b) {
    return $a * $b;
}

Main file:

include "helpers.php";
echo multiply(4, 5); // Outputs: 20

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12. Returning Errors from Functions

Return error indicators (e.g., false, exceptions).

function divide($a, $b) {
    if ($b == 0) {
        return false; // Error indicator
    }
    return $a / $b;
}
$result = divide(10, 0);
if ($result === false) {
    echo "Error: Division by zero!";
} else {
    echo $result;
}
// Outputs: Error: Division by zero!

With exceptions:

function safeDivide($a, $b) {
    if ($b == 0) {
        throw new Exception("Division by zero!");
    }
    return $a / $b;
}
try {
    echo safeDivide(10, 0);
} catch (Exception $e) {
    echo "Error: " . $e->getMessage();
}
// Outputs: Error: Division by zero!

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🔥 Quick Reference

Topic	Key Feature	Example Use Case
Returning Data	Single value	Calculations
Arrays	Multiple values	Data bundles
References	Modify original data	Memory optimization
Static Variables	Persist across calls	Counters
Variable Functions	Dynamic calls	Callbacks
Include Files	Reuse across files	Modular code

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🎯 Best Practices

• Naming: Use clear, verb-based names (e.g., calculateTotal).
• Scope: Minimize global use—pass parameters instead.
• Errors: Prefer exceptions over false for modern code.
• DRY: Don’t Repeat Yourself—use functions to reuse logic.

function formatName($first, $last) {
    return ucfirst($first) . " " . ucfirst($last);
}
echo formatName("john", "doe"); // Outputs: John Doe

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➡️ Next: Reading data