#Program to find factorial of certain number

print("This code was developed by @PythonCoder8 on Github. To see @PythonCoder8's profile go to github.com/PythonCoder8/.")

#Import sys module for verifying user input
import sys

#Ask for user input to enter a number
userInput = input("Enter a number: ")

#If user's input is of float type.....
if isinstance(userInput, float) == True:

    #Exit program with the message "Decimals are not allowed. Only whole numbers are."
    sys.exit("Decimals are not allowed. Only whole numbers are.")

#If error occurs when converting the input to int type, exit program with the message "Your input is not a number."
try:
    userNumber = int(userInput)
except:
    sys.exit("Your input is not a number. Exiting Program.")

#Create a variable named "userProduct", and assign a value of 0
userProduct=1

#Create for loop ranging from 1 to userNumber (variable declared above) + 1, and inside the for loop, ...
for i in range(1,userNumber+1):

    #Keep on adding loop variable to "userProduct"
    userProduct *= i

#Display message showing factorial of number user entered
print("The factorial of %s (!%s) is %d" %(userInput, userInput, userProduct))