Functions in PHP – Reusable Code Blocks

What is a Function in PHP?

A function is a block of code that performs a specific task and can be reused wherever needed.

Instead of repeating the same lines again and again, you can wrap them in a function and call that function when required. This improves code reusability, readability, and maintainability.

Defining a Function in PHP

Syntax:

function functionName() {
  // code to execute
}

function functionName() {
  // code to execute
}

Example:

<?php
function greetUser() {
  echo "Hello, welcome to ScriptBuzz!";
}

greetUser(); // Call the function
?>

<?php
function greetUser() {
  echo "Hello, welcome to ScriptBuzz!";
}

greetUser(); // Call the function
?>

Output:

Hello, welcome to ScriptBuzz!

Hello, welcome to ScriptBuzz!

Function with Parameters

You can pass values to a function using parameters (also called arguments). Parameters are specified inside the parentheses.

Example with One Parameter:

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

greet("Emma");
?>

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

greet("Emma");
?>

Output:

Hello, Emma!

Multiple Parameters:

<?php
function displayUserInfo($name, $age) {
  echo "$name is $age years old.";
}

displayUserInfo("Jay", 28);
?>

<?php
function displayUserInfo($name, $age) {
  echo "$name is $age years old.";
}

displayUserInfo("Jay", 28);
?>

Function with Return Value

Instead of printing the result, you can return it for further use.

Example:

<?php
function getTotal($price, $tax) {
  $total = $price + ($price * $tax / 100);
  return $total;
}

$finalAmount = getTotal(100, 18);
echo "Total Amount: $finalAmount";
?>

<?php
function getTotal($price, $tax) {
  $total = $price + ($price * $tax / 100);
  return $total;
}

$finalAmount = getTotal(100, 18);
echo "Total Amount: $finalAmount";
?>

Output:

Total Amount: 118

Total Amount: 118

Returning values is useful for calculations, validations, and any function whose result you want to reuse.

Default Values in Functions

You can provide default values to parameters. If no value is passed, the default is used.

Example:

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

greet();         // Output: Hello, Guest!
greet("Script"); // Output: Hello, Script!
?>

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

greet();         // Output: Hello, Guest!
greet("Script"); // Output: Hello, Script!
?>

Function Scope – Local vs Global Variables

Local Variables:

Declared inside a function and accessible only within that function.

function testScope() {
  $x = 5; // Local to testScope()
  echo $x;
}

function testScope() {
  $x = 5; // Local to testScope()
  echo $x;
}

Global Variables:

Declared outside a function. To use them inside a function, declare them with the global keyword.

<?php
$x = 10;

function showValue() {
  global $x;
  echo $x;
}
showValue(); // Output: 10
?>

<?php
$x = 10;

function showValue() {
  global $x;
  echo $x;
}
showValue(); // Output: 10
?>

Real-World Examples of PHP Functions

Example 1: Calculate Discount

function calculateDiscount($amount, $discountPercent) {
  return $amount - ($amount * $discountPercent / 100);
}

echo "After Discount: " . calculateDiscount(500, 20);

function calculateDiscount($amount, $discountPercent) {
  return $amount - ($amount * $discountPercent / 100);
}

echo "After Discount: " . calculateDiscount(500, 20);

Example 2: Convert Temperature

function celsiusToFahrenheit($c) {
  return ($c * 9 / 5) + 32;
}

echo celsiusToFahrenheit(30); // Output: 86

function celsiusToFahrenheit($c) {
  return ($c * 9 / 5) + 32;
}

echo celsiusToFahrenheit(30); // Output: 86

Common Mistakes to Avoid

• Declaring the same function name more than once
• Forgetting parentheses when calling a function
• Using variables outside of their scope
• Forgetting the return keyword when needed

Best Practices for Functions

• Name functions clearly (e.g., calculateTotal, sendEmail)
• Keep functions short and focused (one job only)
• Use default values to make functions more flexible
• Always return values if you need to reuse results
• Avoid relying heavily on global variables

otes:

• A function is a reusable block of code that simplifies programming
• Use parameters to pass values and return to send results back
• Functions can have optional/default parameters
• Scope is important: local variables stay within the function
• Functions improve modularity and reduce code repetition

Practice Tasks

Task 1: Greeting Function
Create a function greetUser() that accepts a name and displays:

Hello, [Name]! Welcome to ScriptBuzz.

Hello, [Name]! Welcome to ScriptBuzz.

Task 2: Multiply Function
Write a function that multiplies two numbers and returns the result. Test with 5 and 4.

Task 3: Percentage Calculator
Create a function getPercentage($score, $total) that returns the percentage.