Creation of an EAN-13 barcode generator?

Question

Let's say we have an int with 12 digits. I'll call that int "myCode". Let's say that the value that this int has, is this: 520142909971

From (and including) the 2nd digit, I want to add every other digit. So, I need to store in another int the sum of the digits 2+1+2+0+9+1 and then multiply it by 3 (therefore to get the result of 15 times 3 = 45).

How would I do that?

For those who know more, yes, I am trying to build a code for the calculation of EAN-13 barcodes and to produce a checksum 13th digit.

Answer 1

Try using this function:

int checksum (long long Code)
{
int d; int sum=0;
while(Code!=0)
{
d=Code%10; // Get the last digit.
sum += d;
Code /= 100;
// Remove the last two digits
}
return sum*3;
}