# Factorial Program in PHP with example

Hi friends, in this tutorial, you will learn how to run the factorial program in PHP. I will explain the details in a step-by-step process. This is a very simple program and you will never forget it if you read this article once.

Also, read the OOPs concept in PHP with real-time examples

## Steps to writing the factorial program in PHP

Step 1:- First of all, enter the input value in the HTML form.

Step 2:- Now, we will receive the input value with the help of \$_POST superglobal variable for which the factorial will be calculated.

Step 3:- Next, we will declare some variables as shown below

```\$fact = "";
\$factorial_number_err = "";
```

Step 4:- Now, we will check if the input value is not empty then we will run a for loop up to the number we have received from the HTML form.

Step 5:- Now, each of the incremented values of the for loop will be multiplied with the \$fact variable in every iteration and store the result in the \$fact variable as shown below

Suppose you have to find a factorial of 5, then the for loop will be executed up to 5.

• `For '1', the value of the fact variable will be fact = fact*1 i.e. fact = 1*1 and it becomes face = 1;`
• `For '2', the value of the fact variable will be fact = fact*2 i.e. fact = 1*2 and it becomes fact = 2;`
• `For '3', the value of the fact variable will be fact = fact*3 i.e. fact = 2*3 and it becomes fact = 6;`
• `For '4', the value of the fact variable will be fact = fact*4 i.e. fact = 6*4 and it becomes fact = 24;`
• `For '5', the value of the fact variable will be fact = fact*5 i.e. fact = 24*5 and it becomes fact = 120`

Step 6:- From the above step, you can see that the final factorial value of the entered number is 120.

Complete Code:-

```<?php

\$factorial_number_err = "";
\$fact = "";

if(isset(\$_POST['save']))
{

if(!empty(\$_POST['fact_number']))
{
\$factorial_number = \$_POST['fact_number'];

\$fact = 1;
for(\$i = 1; \$i<=\$factorial_number; \$i++)
{
\$fact = \$i*\$fact;

}
}
else{
\$factorial_number_err = "Input is missing !";
\$fact = "";
}
}
?>
<!DOCTYPE html>
<html lang="en">
<title>Factorial Example</title>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<script src="https://cdn.jsdelivr.net/npm/bootstrap@5.2.1/dist/js/bootstrap.bundle.min.js"></script>
<style type="text/css">
.container{
width: 40%;
}
</style>
<body>
<div class="container mt-3">
<h2>Factorial program in PHP</h2>
<form action="" method="post">
<div class="mb-3 mt-3">
<label for="email" class="fw-bold">Please enter the number:</label>
<input type="number" class="form-control" id="email" placeholder="Enter The Number" name="fact_number">
</div>
<button type="submit" class="btn btn-primary" name="save">Submit</button>
</form>
<br>
<p style="color: red;" class="fw-bold"><?php echo \$factorial_number_err; ?></p>
<?php
if(\$fact!=""){
echo '<p style="color: red;" class="fw-bold">The factorial of the given number is: '.\$fact.'</p>';
}
?>
</div>
</body>
</html>
```