cs50 credit

#include <stdio.h>
#include <string.h>


int addAllDigits(char digits[], int doubleTheDigit) {
    int length = sizeof(digits)/sizeof(digits[0]);
    int finalSum = 0;
    for(int i = 0; i < length; i++) {
        int digit;
        if(doubleTheDigit == 1) {
            digit = (digits[i] - '0')*2;
        } else {
            digit = digits[i] - '0';
        }
        if(digit >= 10) {
            digit = digit/10 + digit%10;
        }
        finalSum += digit;
    }

    return finalSum;
}

int main() {
    char cardNumber[] = "4003600000000014";

    int length = strlen(cardNumber);

    char digits2double[20];
    int digitIndex = 0;
    for(int cardIndex = length-2; cardIndex >= 0; cardIndex -= 2) {
        digits2double[digitIndex] = cardNumber[cardIndex];
        digitIndex++;
    }
    int doubledSum = addAllDigits(digits2double, 1);

    char digits[20];
    digitIndex = 0;
    for(int cardIndex = length-1; cardIndex >= 0; cardIndex -= 2) {
        digits[digitIndex] = cardNumber[cardIndex];
        digitIndex++;
    }
    int sum = addAllDigits(digits, 0);

    printf("--> %d + %d = %d\n", doubledSum, sum, doubledSum + sum);
}