Recursion in PHP with example

Recursion in PHP

In PHP, recursion is a process in which a function calls itself. It is mainly used in those situations where a task can be broken down into smaller, similar tasks. Every recursive function must have two main parts to prevent infinite loops:

• Base Case: A condition that, when met, stops the recursion and returns a value. This is the exit condition.
• Recursive Case: The part of the function that performs the action and calls itself again with modified arguments, moving closer to the base case with each call.

Example: A classic example of recursion is calculating the factorial of a number (n!), which is the product of all positive integers less than or equal to n. The mathematical definition of a factorial is inherently recursive:

• 0! = 1 (Base Case)
• n! = nx(n-1)! (Recursive Case)

<?php 
function factorial(int $n): int {
    // Base Case: Stop the recursion when n is 0 or 1
    if ($n <= 1) {
        return 1;
    } else {
        // Recursive Case: Call the function again with a smaller number
        return $n * factorial($n - 1);
    }
}
$number = 5;
echo "The factorial of $number is: " . factorial($number);
?>

Output:

The factorial of 5 is: 120