Factorial Program using Recursion

Factorial Program using Recursion

In the following Python program, we write a factorial() recursive function. This function returns 1 if the argument is 0 or 1, or calls itself if the number is greater than 1. If the given number is less than 0, then the function shall print a message to the output, and return None.

Python Program

#recursion function
def factorial(n):
    if n < 0:
        print('Invalid input to find factorial.')
    elif n==1 or n==0 :
        return 1
    else :
        return n * factorial(n - 1);  

#read input from user
n = int(input('Enter a number: '))
#call recursion function
result = factorial(n)
#print result
print(result)

Output 1

Enter a number: 5
120

Output 2

Enter a number: 0
1

Output 3

Enter a number: -8
Invalid input to find factorial.
None