A check digit (aka checksum digit) is added to a number, such as book ISBN number or bank routing number, to verify the correctness of the number. The check digit is usually added as the last digit in the number. A common usage of a check digit is to detect errors made while entering the number into a system. For this assignment, you will write a C++ program to generate check digits for ISBN-13 numbers.

The ISBN-13 is a standard, introduced in 2007, for identifying books. It uses 13 digits d₀d₁d₂d₃d₄d₅d₆d₇d₈d₉d₁₀d₁₁d₁₂. The last digit d₁₂ (i.e., the 13^th digit) is check digit that is calculated from the other digits using the following formula:

10 - (d₀ + d₁ * 3 + d₂ + d₃ * 3 + d₄ + d₅ * 3 + d₆ + d₇ * 3 + d₈ + d₉ * 3 + d₁₀ + d₁₁ * 3) % 10

If the checksum is 10, replace it with 0.

Your code must have a function that accepts a string parameter of the first 12-digits in an ISBN-13 number and returns the checksum digit (i.e., the 13^th digit). You may use other functions if you like. For example, a helpful function takes a character containing a digit as parameter and returns that digit as an integer, which you can define as follows:

int toDigit(char ch){ return ch - '0'; // ascii values are subtracted } 

The program must read input from a file, named isbn.txt, that is located in the same folder as the program. Each line on the file contains the first 12-digits of a valid ISBN-13 number. The program outputs to the computer's screen the checksum digit for each number in the file. For example, using the following input file:

978013213079 978032156384 978007063546 978032126817 978145169885 978013213080 978160469555 978032133487 978147926720 

your program should produce the following output:

0 2 3 4 5 6 7 9 0 

Here is code.

#include #include #include

using namespace std;

int checkSum(string s) { istringstream iss(s); long n; int check_digit = 0; iss >> n; while(n > 0) { check_digit = check_digit + (n % 10) * 3; n = n / 10; } check_digit = 10 - (check_digit % 10); check_digit = check_digit % 10; return check_digit; }

int main() { ifstream inFile;

inFile.open("isbn.txt"); string s; while(inFile >> s) cout << checkSum(s) << endl; inFile.close(); return 0; }

But the output is

222222222

Please help me out!!!