Factorial Program

The factorial of a number n is defined by the product of all the digits from 1 to n (including 1 and n).

For example,

4! = 4*3*2*1 = 24
6! = 6*5*4*3*2*1 = 720

Note:

It is denoted by n! and is calculated only for positive integers.
Factorial of 0 is always 1.

The simplest way to find the factorial of a number is by using a loop.

There are two ways to find factorial in PHP:

Using loop
Using recursive method

Logic:

Take a number.
Take the descending positive integers.
Multiply them.

Factorial in PHP

Factorial of 4 using for loop is shown below.

Example:

<?php
$num = 4;
$factorial = 1;
for ($x=$num; $x>=1; $x--) 
{
  $factorial = $factorial * $x;
}
echo "Factorial of $num is $factorial";
?>

Output:

Factorial using Form in PHP

Below program shows a form through which you can calculate factorial of any number.

Example:

<html>
<head>
<title>Factorial Program using loop in PHP</title>
</head>
<body>
<form method="post">
	Enter the Number:<br>
	<input type="number" name="number" id="number">
	<input type="submit" name="submit" value="Submit" />
</form>
<?php 
	if($_POST){
		$fact = 1;
		//getting value from input text box 'number'
		$number = $_POST['number'];
		echo "Factorial of $number:<br><br>";
		//start loop
		for ($i = 1; $i <= $number; $i++){		
			$fact = $fact * $i;
			}
			echo $fact . "<br>";
	}
?>
</body>
</html>

Output:

Factorial using Recursion in PHP

Factorial of 6 using recursion method is shown.

Example:

<?php
function fact ($n)
{
    if($n <= 1) 
    {
        return 1;
    }
    else 
    {
        return $n * fact($n - 1);
    }
}

echo "Factorial of 6 is " .fact(6);
?>

Output: