Question

Exercise: Finding the Factorial Write a program so a user enters a positive integer N and outputs N1 (meaning N factorial, given by N (N-1) (N-2) 2 1) Hint: Initialize a variable total to N (where N is input), and use a loop variable i that counts from total 1 down to 1 Compare your output with some of these answers 1 1, 21 2, 316, 4! 24, 5 120, 8! 40320 Ref: zyDE 5.4.3 of your zyBook My Solution

***answer using pythin***

***include indentation in the program if necessary***

Answer 1

Pre-requisite:

1) Code is been run in python 3

2) You have "sys" and "re" modules installed in your python version

How to run the program:

Save the provided code in some file and execute the saved file using python interpreter. The script will accept a single input on every run thus execute the script for every different input.

below is the snip when you execute the script:

$ ./factorial.py Enter a positive integer: 3

You can see above that on executing the script it prompts for the input, and I have provided "3" as input, as soon as you provide the input, press enter and you would see the result on you console.

CODE PASTED AS BELOW

fron sys import exit import re def checkInt(iten): # check if the value is an integer or not # return True if an positive integer # else return false if not an integer # we are also excluding 'O' from the allowed inputs if item.isdigit() and int(iten) != 0: return True elif re.match(r"\d+\. *\d*", iter) or re.match(r"-\d+\. *\d*", iten): return false else: return false # Accept an value as input from the user N = input("Enter a positive integer: ") # check if the provided input is a positive non-zero integer if not checkInt(N): # if not a valid input then print the error nessage and exit the script print("Please enter a positive integer") exit(1) # store the value into a teap variable to be used later in printing the output nur = N # initialize the factorial variable to be equal to the value been input # also doing an int assignnent to "fact" variable so that later on there is no type error while # perforaing nathematical operations fact = int(N) # looping until the input value is not zero, as we would be subtracting the # input integer by 1 on every iteration while N != 0 : # in case the value is 1 then we break from the loop, as we do not want to further # decrenent the number as if done then the resultant will come to zero if int(N) == 1: break # fact variable was assigned the value of the input integer before the start of this while block # lets suppose 6 was entered as input then 'fact' variable got an assignment to 6 before this while block # now below line will just go on multiplying the decresented input integer value on each iteration # thus this will further go on storing as 5 * 4 * 3 * 2 ( assuming 6 was the input string ) fact = fact * (int(N) - 1) # decrenent the value of 'N' by 1 on each iteration N = int(N) - 1 # print the factorial result print("%s! = %d %(nur, fact))

OUTPUT OF THE PROGRAM:

$ ./factorial.py Enter a positive integer: 1 1! = 1 $ ./factorial.py Enter a positive integer: 2 2! = 2 $ ./factorial.py Enter a positive integer: 3 3! = 6 $ ./factorial.py Enter a positive integer: 4 4! = 24 $ ./factorial.py Enter a positive integer: 5 5! = 120 $ ./factorial.py Enter a positive integer: 8 8! = 40320

CODE TO COPY:

from sys import exit

import re

def checkInt(item):

        # check if the value is an integer or not

        # return True if an positive integer

        # else return False if not an integer

        # we are also excluding '0' from the allowed inputs

        if item.isdigit() and int(item) != 0:

                return True

        elif re.match(r"\d+\.*\d*", item) or re.match(r"-\d+\.*\d*", item):

                return False

        else:

                return False

# Accept an value as input from the user

N = input("Enter a positive integer: ")

# check if the provided input is a positive non-zero integer

if not checkInt(N):

        # if not a valid input then print the error message and exit the script

        print("Please enter a positive integer")

        exit(1)

# store the value into a temp variable to be used later in printing the output

num = N

# initialize the factorial variable to be equal to the value been input

# also doing an int assignment to "fact" variable so that later on there is no type error while

# performing mathematical operations

fact = int(N)

# looping until the input value is not zero, as we would be subtracting the

# input integer by 1 on every iteration

while N != 0:

        # in case the value is 1 then we break from the loop, as we do not want to further

        # decrement the number as if done then the resultant will come to zero

        if int(N) == 1:

                break

        # fact variable was assigned the value of the input integer before the start of this while block

        # lets suppose 6 was entered as input then 'fact' variable got an assignment to 6 before this while block

        # now below line will just go on multiplying the decremented input integer value on each iteration

        # thus this will further go on storing as 5 * 4 * 3 * 2 ( assuming 6 was the input string )

        fact = fact * (int(N) - 1)

        # decrement the value of 'N' by 1 on each iteration

        N = int(N) - 1

# print the factorial result

print("%s! = %d" %(num,fact))