Luhn algorithms in C cs50

Question

#include <cs50.h>
#include <stdio.h>
int main(void)
{
    long firsttwodig;
    long cardnumber;
    int sum = 0;
    int count = 0;
    cardnumber = get_long("card number:");

    firsttwodig = cardnumber;




        //first case of luhn alg
        int workingcc = cardnumber;
        while(workingcc > 0)
        {
            int lastdig = workingcc % 10;
            sum = sum + lastdig;
            workingcc = workingcc / 100;

        }


        //secound case of luhn alg
        workingcc= cardnumber / 10;
        while(workingcc > 0)
        {
            int lastdig = workingcc % 10;
            int timestwo = lastdig * 2;
            sum = sum +(timestwo % 10) + (timestwo / 10);
            workingcc = workingcc / 100;

so this is half of the code but the part where it wont work i tried everything but the luhn algo part just wont work for some reasone the code it self works its just everything is invalid thans in advanced

Jwan Kamal, save time and enable all warnings and see trouble with `int workingcc = cardnumber;`, More productive than posting on SO, — chux - Reinstate Monica, Nov 13 '22 at 05:44
Please clarify your specific problem or provide additional details to highlight exactly what you need. As it's currently written, it's hard to tell exactly what you're asking. — Community, Nov 13 '22 at 19:12

score 0 · Answer 1 · answered Nov 13 '22 at 02:58

Hello.

I took your code and added in some code that was missing at the end of your pasted text, and then sprinkled in a few print statements to do a quick manual debug of the process.

Basically, your only issue is that you need to also define your credit card work field to be long integers as well. Instead of:

int workingcc = cardnumber;

You should have:

long workingcc = cardnumber;

When I tweaked that bit of code, I got the following type of terminal output.

@Dev:~/C_Programs/Console/Loon/bin/Release$ ./Loon 
Enter card number: 5555555555555555
Working number: 555555555555555
Times two: 10
Times two: 10
Times two: 10
Times two: 10
Times two: 10
Times two: 10
Times two: 10
Times two: 10
The sum is: 48 which is invalid
@Dev:~/C_Programs/Console/Loon/bin/Release$ ./Loon 
Enter card number: 5555555555555557
Working number: 555555555555555
Times two: 10
Times two: 10
Times two: 10
Times two: 10
Times two: 10
Times two: 10
Times two: 10
Times two: 10
The sum is: 50 which is valid
@Dev:~/C_Programs/Console/Loon/bin/Release$

The output agreed with an online Luhn algorithm check utility.

Give that a try.

that worked for me as soon as i made it into a long type thanks for taking ur time to help me :) — Jwan Kamal, Nov 13 '22 at 14:47

Luhn algorithms in C cs50

1 Answers1