PHP Functions
Reusable blocks of code that perform specific tasks
🔧 What are PHP Functions?
Functions are reusable blocks of code that perform specific tasks. They help organize code, reduce repetition, and make programs easier to maintain and understand.
<?php
// Simple function example
function greet() {
echo "Hello, World!";
}
greet(); // Call the function
?>
Output:
Hello, World!
Types of Functions
Built-in Functions
PHP provides thousands of ready-to-use functions for common tasks like string manipulation, math operations, and array handling.
<?php
echo strlen("Hello"); // 5
echo strtoupper("php"); // PHP
?>User-Defined Functions
Create your own custom functions to perform specific tasks. Define once and reuse throughout your code for better organization.
<?php
function sayHello() {
echo "Hello!";
}
?>Functions with Parameters
Pass data to functions using parameters. This makes functions flexible and able to work with different values each time.
<?php
function greet($name) {
echo "Hello, $name!";
}
?>Return Values
Functions can return values using the return statement. This allows you to use the result in other parts of your code.
<?php
function add($a, $b) {
return $a + $b;
}
?>🔹 Creating Basic Functions
Define a function using the
function
keyword:
<?php
// Function without parameters
function displayMessage() {
echo "Welcome to PHP Functions!";
}
// Call the function
displayMessage();
?>Output:
Welcome to PHP Functions!
🔹 Functions with Parameters
Pass information to functions using parameters:
<?php
// Function with one parameter
function greetUser($name) {
echo "Hello, $name! Welcome back.";
}
greetUser("Alice");
echo "<br>";
greetUser("Bob");
?>Output:
Hello, Alice! Welcome back.
Hello, Bob! Welcome back.
🔹 Multiple Parameters
Functions can accept multiple parameters separated by commas:
<?php
function calculateSum($num1, $num2) {
$sum = $num1 + $num2;
echo "$num1 + $num2 = $sum";
}
calculateSum(10, 20);
echo "<br>";
calculateSum(5, 15);
?>Output:
10 + 20 = 30
5 + 15 = 20
🔹 Default Parameter Values
Set default values for parameters if no argument is provided:
<?php
function greetWithTitle($name, $title = "Guest") {
echo "Hello, $title $name!";
}
greetWithTitle("Smith", "Mr.");
echo "<br>";
greetWithTitle("Johnson"); // Uses default "Guest"
?>Output:
Hello, Mr. Smith!
Hello, Guest Johnson!
🔹 Return Values
Use
return
to send a value back from a function:
<?php
function multiply($a, $b) {
return $a * $b;
}
$result = multiply(5, 4);
echo "5 × 4 = $result";
// Use directly in expressions
echo "<br>";
echo "10 × 3 = " . multiply(10, 3);
?>Output:
5 × 4 = 20
10 × 3 = 30
🔹 Variable Scope
Variables inside functions have local scope and can't be accessed outside:
<?php
$globalVar = "I'm global";
function testScope() {
$localVar = "I'm local";
echo $localVar . "<br>";
// Access global variable using 'global' keyword
global $globalVar;
echo $globalVar;
}
testScope();
// echo $localVar; // This would cause an error
?>Output:
I'm local
I'm global
🔹 Common Built-in Functions
PHP provides many useful built-in functions:
<?php
// String functions
echo strlen("Hello"); // Length: 5
echo "<br>";
echo strtoupper("hello"); // HELLO
echo "<br>";
echo str_replace("World", "PHP", "Hello World"); // Hello PHP
echo "<br><br>";
// Math functions
echo abs(-15); // 15
echo "<br>";
echo round(4.7); // 5
echo "<br>";
echo max(2, 8, 5, 1); // 8
?>Output:
5
HELLO
Hello PHP
15
5
8
🔹 Practical Example
Create a simple calculator using functions:
<?php
function calculate($num1, $num2, $operation) {
switch($operation) {
case 'add':
return $num1 + $num2;
case 'subtract':
return $num1 - $num2;
case 'multiply':
return $num1 * $num2;
case 'divide':
return $num2 != 0 ? $num1 / $num2 : "Cannot divide by zero";
default:
return "Invalid operation";
}
}
echo "10 + 5 = " . calculate(10, 5, 'add');
echo "<br>";
echo "10 - 5 = " . calculate(10, 5, 'subtract');
echo "<br>";
echo "10 × 5 = " . calculate(10, 5, 'multiply');
echo "<br>";
echo "10 ÷ 5 = " . calculate(10, 5, 'divide');
?>Output:
10 + 5 = 15
10 - 5 = 5
10 × 5 = 50
10 ÷ 5 = 2
💡 Function Best Practices:
- Descriptive Names: Use clear names that describe what the function does
- Single Purpose: Each function should do one thing well
- Keep it Short: Functions should be concise and focused
- Use Comments: Document complex functions with comments
- Return Values: Return values instead of echoing when possible