Chapter 5: Functions and Includes: Reusable Code in PHP

In this chapter, we will explore functions and includes in PHP, which allow us to write reusable code. We will cover defining and calling functions, passing arguments to functions, returning values from functions, and including external files in our PHP scripts.

5.1 Defining and calling functions:

Functions are blocks of code that perform specific tasks and can be reused throughout our program.

We define functions using the function keyword, followed by the function name and a pair of parentheses.

We call functions by using their name followed by a pair of parentheses.

Example:

php

""

<?php

   // Function definition

   function greet() {

       echo "Hello, World!";

   }

   

   // Function call

   greet(); // Output: Hello, World!

?>

5.2 Passing arguments to functions:

Arguments allow us to pass data to functions, making them more flexible and customizable.

We can define parameters in the function's parentheses and provide values for those parameters when calling the function.

Example:

php

""

<?php

   // Function definition with parameter

   function greet($name) {

       echo "Hello, " . $name . "!";

   }

   

   // Function call with argument

   greet("John"); // Output: Hello, John!

?>

5.3 Returning values from functions:

Functions can return values using the return statement.

The returned value can be stored in a variable or used directly in our code.

Example:

php

""

<?php

   // Function definition with return value

   function multiply($num1, $num2) {

       $result = $num1 * $num2;

       return $result;

   }

   

   // Function call and storing the return value

   $product = multiply(5, 3);

   echo $product; // Output: 15

?>

5.4 Including external files:

Including external files allows us to reuse code across multiple PHP scripts.

We can use the include or require statement to include an external file.

The difference between include and require is that require will produce a fatal error if the file cannot be included, while include will only produce a warning.

Example:

Suppose we have a file named utils.php with the following code:

php

""

<?php

   function add($num1, $num2) {

       return $num1 + $num2;

   }

?>

We can include this file in our main PHP script as follows:

php

""

<?php

   // Including the external file

   include 'utils.php';

   

   // Using the function from the included file

   $sum = add(2, 3);

   echo $sum; // Output: 5

?>

By following the explanations and examples in this chapter, you will gain a solid understanding of functions and includes in PHP, allowing you to write reusable code and organize your scripts more efficiently.