Question

Please do it in c++ please show steps as much as possible to help me understand the code thank you

Credit Card error detection check -> Luhn Algorithm, (http://www.freeformatter.com/credit-card-number-generator-validator.html#cardFormats)

From the rightmost digit, which is the check digit, moving left, double the value of every second digit; if the product of this doubling operation is greater than 9 (e.g., 7 * 2 = 14), then sum the digits of the products (e.g., 10: 1 + 0 = 1, 14: 1 + 4 = 5).

Take the sum of all the digits. If the total modulo (Links to an external site.)Links to an external site. 10 is equal to 0 (if the total ends in zero) then the number is valid according to the Luhn formula; else it is not valid.

Assume an example of an account number "7992739871" that will have a check digit added, making it of the form 7992739871x:

Account number	7	9	9	2	7	3	9	8	7	1	x
Double every other	7	18	9	4	7	6	9	16	7	2	x
Sum of digits	7	9	9	4	7	6	9	7	7	2	=67

The check digit (x) is obtained by computing the sum of digits then computing 9 times that value modulo 10 (in equation form, (67 * 9 mod 10)). In algorithm form:

Compute the sum of the digits (67).

Multiply by 9 (603).

The last digit, 3, is the check digit.

Answer 1

Code in C++:

#include<iostream>
using namespace std;
int main()
{
   string accNum;
   cout << "Enter account number: ";
   cin >> accNum;
   int sum=0;
   //Iterate entire account number
   for(int i=0;i<accNum.length();i++)
   {
       //convert digit to number
       int digit= accNum.at(i) - '0';
       //double thedigits at odd positions
       if(i%2!=0)
       {
           //After doubling the digit if it is greater than 9 then remove 9 from it
           if(2*digit>9)
               sum = sum + (2*digit-9);
           //Else just add double of digit
           else
               sum=sum+2*digit;
       }
       //Add digits at even positions
       else
           sum=sum+digit;
   }
   //find last digit x which satisifies our conditions
   for(int x=0;x<10;x++)
   {
       //If sum+x divisible by 10 then print it and break
       if((sum+x)%10==0)
       {
           //output
           cout << "The last digit, "<< x <<", is the check digit."<<endl;
           break;
       }
   }
   return 0;
}

output screenshot: On multiple screens