### Credit Card Validation Question

Hello,

I have an assignment where I need to write a program to validate a credit card using the LUHN formula (MOD10). I have steps on what to do but I'm lost on the first two.

Step 1: Double the value of alternate digits of the primary account number beginning with the second digit from the right.

Step 2: Add the individual digits comprising the products obtained in Step 1 to each of the unaffected digits in the original number.

I'm not sure how to go about doing either of those two steps. Also note that the 6 credit cards numbers that are being provided I'm reading in from another file. I've got that part its what to do after I get the numbers into my program where I lose it.

Any help would be great!

 ``1234567891011121314151617181920212223`` ``````#include #include int main() { // get the digit at position pos // (counting towards left with the right most digit at position zero) const std::size_t pos = 7 ; // from a string const std::string numstr = "9876543210" ; const std::size_t sz = numstr.size() ; int digit = pos < sz ? numstr[ sz - 1 - pos ] - '0' : 0 ; std::cout << "digit at position " << pos << " from the right is " << digit << '\n' ; // from an unsigned long long const unsigned long long number = 9876543210 ; int divisor = 1 ; for( std::size_t i = 0 ; i < pos ; ++i ) divisor *= 10 ; digit = ( number / divisor ) % 10 ; std::cout << "digit at position " << pos << " from the right is " << digit << '\n' ; }``````