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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)
The factorial of 7 is 5040
Note: To test the program for a different number, change the value of
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.