Find the Factorial of a Number

The factorial of a number is the product of all the integers from 1 to that number. For example, the factorial of 6 (denoted as 6!) is 1*2*3*4*5*6 = 720. Factorial is not defined for negative numbers and the factorial of zero is one, 0! = 1.

Source Code

# Python program to find the factorial of a number provided by the user.

# take input from the user
num = int(input("Enter a number: "))
factorial = 1

# check if the number is negative, positive or zero
if num < 0:
   print("Sorry, factorial does not exist for negative numbers")
elif num == 0:
   print("The factorial of 0 is 1")
else:
   for i in range(1,num + 1):
       factorial = factorial*i
   print("The factorial of",num,"is",factorial)

Output 1

Enter a number: -2
Sorry, factorial does not exist for negative numbers

Output 2

Enter a number: 7
The factorial of 7 is 5040

Here, we take input from the user and check if the number is negative, zero or positive using if...elif...else statement. If the number is positive, we use for loop and range() function to calculate the factorial.