# Problem - CS50x Credit Pset1

I'm currently three lectures into cs50 as a completely new programmer and I am enjoying it tremendously!

I've enjoyed struggling on mario(less/more comfortable) and cash but right now I'm at a complete loss with credit pset1. My code is hitting a brick wall at the end and I'm not sure how to continue.

The problem im facing is that after printing out the second from last digits in a given input, I'm not sure how to "save" these digits so that I can multiply them by two and add them together to validate the credit card number...

Would appreciate any form of input!

#import <cs50.h>
#import <stdio.h>

int main(void)
{
long long x;

// Prompts for positive integer from user

do
{
x = get_long_long("Number: ");
}

while (x < 0);

// Create new integer variable (y) to represent number of digits(initializes at zero)

int y = 0;

// Create new variables for use later on...
// long long (h) will be used to store input value of x since value of x will be manipulated to find digits later...
// long long (z) will be used as a temp placeholder for future variable t,
// long long (t) will be used in conjunction with mod 10 in a simple formula to find the second last digit...

long long h;
h = x;
long long z = h / 10;
long long t;

// Find number of digits in user's value by creating while loop(digit count+1 after every division by 10)

while (x > 0)
{
x /= 10;
y ++;
}

printf("Amount of digits: %d\n", y);

// Run validity check based on amount of digits

if ((y != 13) && (y != 15) && (y != 16))
{
printf("INVALID\n");
}

// Create for loop to print every second digit starting from the last
for (int p = 1; p < y; p++)
{
t = z % 10;
printf("%lld\n", t);
z /= 100;
}

}