The factorial of a number is the product of all the integers from 1 to that number.
For example, the factorial of 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
.
Factorial of a Number using Loop
# Python program to find the factorial of a number provided by the user.
# change the value for a different result
num = 7
# To 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
The factorial of 7 is 5040
Note:
To test the program for a different number, change the value of
num
.
Here, the number whose factorial is to be found is stored in
num
, and we 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.
iteration | factorial*i (returned value) |
i = 1 | 1 * 1 = 1 |
i = 2 | 1 * 2 = 2 |
i = 3 | 2 * 3 = 6 |
i = 4 | 6 * 4 = 24 |
i = 5 | 24 * 5 = 120 |
i = 6 | 120 * 6 = 720 |
i = 7 | 720 * 7 = 5040 |
Factorial of a Number using Recursion
# Python program to find the factorial of a number provided by the user
# using recursion
def factorial(x):
"""This is a recursive function
to find the factorial of an integer"""
if x == 1:
return 1
else:
# recursive call to the function
return (x * factorial(x-1))
# change the value for a different result
num = 7
# to take input from the user
# num = int(input("Enter a number: "))
# call the factorial function
result = factorial(num)
print("The factorial of", num, "is", result)
In the above example,
factorial()
is a recursive function that calls itself. Here, the function will recursively call itself by decreasing the value of the
x
.
To learn about the working of recursion, visit Python recursion .