# Python Program Find Factorial Of A Number

The factorial of a number is the product of all the integers from 1 to that number. Mathematically, the formula for the factorial is as follows. If n is an integer greater than or equal to 1, then factorial of n is,

` (n!) = 1*2*3*4....*n`

Also, the factorial value of 0 is equal to 1 and the factorial values for negative integers are not defined.

## Problem Definition

Create a Python Program to find the factorial of the user-provided number.

## Program

```
num = int(input("Enter the Number :"))
fact = 1
if num < 0:
print("Factorial of negative number is not defined")
else:
for i in range(1,num+1):
fact *= i
print("Factorial of {} is {}".format(num, fact))
```

#### Output

```
Enter the Number :7
Factorial of 7 is 5040
```

In this program first, we are taking input from the keyboard using the `input()`

function then we have a conditional statement for negative inputs since factorial of a negative number doesn’t exist.

Then we have a for loop in range 1 to the number itself inside the loop we are simply iterating over loop variable `i`

and multiplying it with the `fact`

variable defined above. In the end, we are simply printing out the result using string formatting.

The same program can be implemented using a while loop as follows,

```
num = int(input("Enter the Number :"))
fact = 1
i = 1
if num < 0:
print("Factorial of negative number is not defined")
else:
while(i<=num):
fact *= i
i += 1
print("Factorial of {} is {}".format(num, fact))
```

#### Output

```
Enter the Number :6
Factorial of 6 is 720
```

Since Python always has a better way of doing things, it comes with a built-in solution for computing factorial of a number.

```
from math import factorial
num = int(input("Enter the Number :"))
fact = factorial(num)
if num < 0:
print("Factorial of negative number is not defined")
else:
print("Factorial of {} is {}".format(num, fact))
```

#### Output

```
Enter the Number :5
Factorial of 5 is 120
```

The `math`

library which ships with Python has a `factorial()`

method that returns the factorial of the provided number.

Thanks for such a beautiful post, very informative and useful article