Simple Factorial Program in PHP

The factorial of a number is the product of all integers up to and including that number, so the factorial of 4 is 4*3*2*1= 24.

<?php
// Formula: n! = n*(n-1)*(n-2)*(n-3)...3.2.1 and zero factorial is defined as one i.e. 0! = 1.

// Method 1. Using for loop
$fact = 1;
$number = 5;

for ($i = 1; $i <= $number; $i++)
    $fact = $fact * $i;

echo $fact;

//----------------------------------
// Method 2: Using recursive method

function factorial($n) {
    if ($n == 0)
        return 1;
    else
        return($n * factorial($n - 1));
}
$number=6;
echo factorial($number);
?>