#include <cs50.h>
#include <stdio.h>

int main(void)
{
    long number = get_long("Type in your credit card number!\n");
    long new_num = number;
    int odd_num = 0;
    int odd_sum = 0;
    int even_sum = 0;
    int card_length = 0;

    //copy number to use to get length
    long new_num_copy = new_num;

    int length = 0;
    while(new_num_copy > 0){
        length++;
        new_num_copy /= 10; // divide by 10 until you get to 0, the times you do that, is the length
    } // variable length will be the lenth of new_num by the end of this

    int first_num = 0; //first number from the left
    int second_num = 0; //second number from the left

    for (int i = length; i > 0; i--)
    {
        //first condition for odd length numbers second for even length numbers
        if((i == 1 && length % 2 != 0) || (i == 2 && length % 2 == 0)){
            second_num = new_num  % 10; //if we hit the end, save second number
        }

        even_sum += (new_num  % 10);
        new_num /= 10;

        //first condition for odd length numbers second for even length numbers
        if((i == 3 && length % 2 != 0) || (i == 2 && length % 2 == 0)){
            first_num = new_num % 10; //if we hit the end, save first number too
        }

        i--; // decrease again because we do new_num / 10 twice, shortening the numbers length, so just skip one step

        //odd_num calculation starts here
        odd_num += ((new_num % 10) * 2);
        new_num /= 10;
        for (int j = 0; j < sizeof(odd_num); j++)
        {
            odd_sum += (odd_num % 10);
            odd_num /= 10;
        }
    }

    if(length % 2 != 0){ //Switch them if length is odd, they are backwards when it's odd
        int temp = first_num;
        first_num = second_num;
        second_num = temp;
    }

    printf("\n%i -- %i\n",odd_sum,even_sum); //print the sums
    printf("\n%i -- %i\n",first_num,second_num); //print the first and second number

    if ((odd_sum + even_sum) % 10 == 0) //final result and display error message if needed
    {
        return true;
    } else {
        printf("Card not valid!\n");
        return false;
    }
}