## Description

In this tutorial, we are going to learn a python program to find the factorial of the number given as input from the user.

## Problem Statement

For any numbers that are input by the user, we have to calculate the factorial of that numbers.

**For example**

**Case1:** If the user input the 5.

then the output should be 120 ( 1*2*3*4*5= 120).

**Case2:** If the user input the 6.

then the output should be 720 (1*2*3*4*5*6 =720).

## What is Factorial of a number?

The factorial of a number is the multiplication of each and every number till the given number except 0.

**For example**

**Case 1**: factorial of number 4 is the multiplication of every number till number 4, i.e. 1*2*3*4

**Case 2**: factorial of number 3 is the multiplication of every number till number 3, i.e. 1*2*3

**Note**

*The factorial of 0 is 1**The factorial of any negative number is not defined.**The factorial only exits for whole numbers.*

## Our logic to find factorial

- Our program will take an integer input from the user which should be a whole number.
- If the number input is negative then print ‘The factorial can’t be calculated’.
- Then use
**for**loop with**range**function to define the sequence of numbers which we will use to calculate the factorial. - After that, we will store the value of the factorial in a variable and finally print the value of the variable.

## Algorithm of Factorial Program In Python

Step 1: Start

Step 2: take input from the user for finding the factorial.

Step 3: Create a variable ‘factorial’ and assign the value 1.

Step 4: if(number<0):

print ‘cannot be calculated.

elif ( number == 1):

print 1

else:

for i in range(1, number+1):

factorial*=i

Step 5: print factorial

Step 6: Stop

Let’s code the above algorithm in the python programming language.

## Python program to calculate the factorial

#taking an integer input from user num=int(input("Enter the whole number to find the factorial: ")) factorial = 1 if num < 0: print("Factorial can't be calculated for negative number") elif num == 0: print("Factorial of 0 is 1") else: #calculating the factorial of the input number for i in range(1,num + 1): factorial = factorial*i print("Factorial of",num,"is",factorial)

**Output** **1:**

**Explanation of the above factorial output**

The input number from the user to find the factorial is 5. The calculated value of the factorial is 1*2*3*4*5.

**Output 2:**

**Explanation of the above factorial output**

The input number from the user to find the factorial is 8. The calculated value of the factorial is 1*2*3*4*5*6*7*8.

[wpusb]