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Recursion

Explore how recursion works in PHP by learning how functions call themselves with a base case to avoid infinite loops. Understand the factorial example step-by-step, compare recursion with iteration, and recognize recursion's memory impact for better programming decisions.

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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
<?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 ...