deepyes02/factorial.php

## factorial.php
<!DOCTYPE html>
<html lang="en">
<head>
	<meta charset="UTF-8">
	<meta http-equiv="X-UA-Compatible" content="IE=edge">
	<meta name="viewport" content="width=device-width, initial-scale=1.0">
	<title>Factorial</title>
</head>
<body>
<h2>Find Factorial</h2>
<form action="<?php echo $_SERVER['PHP_SELF'] ?>" method='POST'>
	<label for="user_input">Enter a Number</label>
	<input type="number" name="user_input" value=<?php echo isset($_POST['user_input']) ? $_POST['user_input'] : '' ?> />
	<input type="submit" />
	<br>
	<?php if (isset($_POST['user_input'])) : ?>
		<h5><?php echo factorial($_POST['user_input']) ?></h5>
	<?php endif; ?>
</form>

<?php
/**
 * Calculate and return factorial of any given number
 * @param int $n - any valid number
 * @return int - when input is valid
 * @return string - when input is less than zero, i.e, negative
 */
function factorial(int $n)
{
	# logic for when input is less than or equal to zero
	if ($n <= 0) # return string invalid for number less than 0, and 1 for 0 and 1.
	{
		# returns invalid for negative number, and 1 for the rest of the possibility.
		# because of the if ($n <= 0) block, the only possible conditionals are either negative or zero here.
		return $n < 0 ? "Invalid, range is 0 ~ ..." : intval(1);
	}
	//validation ends, start the logic for valid whole numbers, e.g 4
	# this block will keep a check on the function for the value of run
	# and will execute when n is reduced to 1 by the following recursive function right after the code.
	if ($n == 1) {
		return $n;
	}

	#recursive function.
	# smartly grabs the number and calls the function with one less, if not checked by if ($n == 1)
	# this function will run indefinitely and cause fatal error
	return $n * factorial(intval($n - 1));
}
?>

<script src="https://gist.github.com/deepyes02/3e851e1d6e38325971b443ffdc9eed62.js"></script>
</body>
</html>
	<!DOCTYPE html>
	<html lang="en">
	<head>
	<meta charset="UTF-8">
	<meta http-equiv="X-UA-Compatible" content="IE=edge">
	<meta name="viewport" content="width=device-width, initial-scale=1.0">
	<title>Factorial</title>
	</head>
	<body>
	<h2>Find Factorial</h2>
	<form action="<?php echo $_SERVER['PHP_SELF'] ?>" method='POST'>
	<label for="user_input">Enter a Number</label>
	<input type="number" name="user_input" value=<?php echo isset($_POST['user_input']) ? $_POST['user_input'] : '' ?> />
	<input type="submit" />
	<br>
	<?php if (isset($_POST['user_input'])) : ?>
	<h5><?php echo factorial($_POST['user_input']) ?></h5>
	<?php endif; ?>
	</form>

	<?php
	/**
	* Calculate and return factorial of any given number
	* @param int $n - any valid number
	* @return int - when input is valid
	* @return string - when input is less than zero, i.e, negative
	*/
	function factorial(int $n)
	{
	# logic for when input is less than or equal to zero
	if ($n <= 0) # return string invalid for number less than 0, and 1 for 0 and 1.
	{
	# returns invalid for negative number, and 1 for the rest of the possibility.
	# because of the if ($n <= 0) block, the only possible conditionals are either negative or zero here.
	return $n < 0 ? "Invalid, range is 0 ~ ..." : intval(1);
	}
	//validation ends, start the logic for valid whole numbers, e.g 4
	# this block will keep a check on the function for the value of run
	# and will execute when n is reduced to 1 by the following recursive function right after the code.
	if ($n == 1) {
	return $n;
	}

	#recursive function.
	# smartly grabs the number and calls the function with one less, if not checked by if ($n == 1)
	# this function will run indefinitely and cause fatal error
	return $n * factorial(intval($n - 1));
	}
	?>

	<script src="https://gist.github.com/deepyes02/3e851e1d6e38325971b443ffdc9eed62.js"></script>
	</body>
	</html>