Learn PHP basics with hands-on practice in hello world in PHP, variables in PHP, functions in PHP, arrays in PHP, PHP inheritance, PHP exceptions, and more.

This interactive course introduces you to the fundamentals of PHP programming, one of the most widely used languages in web development. Starting with a simple hello world in PHP, you’ll explore the basics, including PHP output, variables in PHP, and PHP data types. You’ll also learn about PHP constants, arithmetic operators, comparison operators, logical operators, and assignment operators.

The course progresses into conditional statements in PHP, PHP switch, and various loops such as PHP for loop, PHP while loop, and more. You will then dive deeper into functions in PHP, understand PHP variable scope, and learn PHP pass by reference or value. Additionally, you’ll gain a working knowledge of strings in PHP, PHP string operations, and handling arrays in PHP, including PHP multidimensional arrays.

In the advanced sections, you’ll explore classes in PHP, inheritance, constructors, and destructors, handling PHP exceptions with PHP throw and catch exceptions.

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# What is Recursion?
*Recursion* is a method of function *calling* in which a function calls *itself* during execution. 

A recursive function must comprise of at least one base case i.e. a condition for termination of execution. 

The function keeps on converging to the defined base case as it continuously calls itself.

## Example
Let's start by showing an example and then discussing it.

<?php
function factorial($n)
{
    if ($n == 1 || $n == 0)
    { //base case
        return 1;
    }
    else
    {
        return $n * factorial($n - 1); //function calls itself
        
    }
}

echo factorial(4); //calling the function with 4 as the argument

?>


This is a classic application of *recursion*. This function calculates the **factorial** of a number. 

>**Note:** The *factorial* of **n**, written **n!**, is the product of every number from **1 to n**. So we can say that **4! = 4×3×2×1**.

## Solution Explained

Let's step through what happens in our *function* when we call `factorial(4)`.

* In **line 11**, `factorial(4)` is called
    * Inside the `factorial` function, since, **n=4** we take the `else` path. We `return` `4×factorial(n-1)`, **line 7**.
    * `factorial(3)` is called
             
      * Since **n=3**, we take the `else` path. We return `3×factorial(n-1)`,  **line 7**.
       * `factorial(2)` is called
            * Since **n=2**, we take the `else` path. We return `2×factorial(n-1)`, **line 7**.
            * `factorial(1)` is called
              * Since **n=1**, we take the *first* path, **line 3**, and finally return **1** to the *previous* function.
         * `factorial(1)` returns **1** so `factorial(2)` can return **2×1...2**.
      * `factorial(2)` returns **2** so `factorial(3)` can return **3×2...6**.
  * `factorial(3)` returns **6** so `factorial(4)` can return **4×6...24**.  

Many times, a *recursive* solution to a problem is very easy to program. 

* The drawback of using *recursion* is that there is a lot of *overhead*. 

Every time a function is called, it is placed in *memory*. Since you don't **exit** the `factorial` function until **n** reaches **1**, **n** functions will reside in *memory*. This isn't a problem with the simple `factorial(4)`, but other functions can lead to serious memory requirements.  

# Recursion versus Iteration

>**Iteration** is a sequence of steps that are executed *repeatedly* until a certain condition is met. 

The steps may or may not be enclosed in a function. 

However, in recursion, the function itself is called repeatedly as done in the `factorial` example above.

The following figure illustrates the difference between *recursion* and *iteration*:

This lesson explains the concept of recursion using the factorial example

PHP Basics

PHP Variables

PHP Operators

PHP Conditional Statements

PHP Loops

PHP Functions

PHP Strings

PHP Arrays

PHP Assessment 1

PHP Classes

Exception Handling in PHP

PHP Assessment 2

Recursion