# Check50 giving different results from the code I compiled in pset1

For Problem Set 1, I have the code as written below

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

int card_length(long cNo);
void luhn_algo(long lacno, int lacnolen);
void finalPrint(int cardDet);

int main(void)
{
//Get user input of card number
long cardNo = get_long("Number: ");
int ct = card_length(cardNo);

//Check if card no is length 13, 15 or 16
if (ct == 13 || ct == 15 || ct == 16)
{
luhn_algo(cardNo, ct);
}
else
{
// Invalid due to unacceptable length
printf("INVALID\n");
}
return 0;
}

//Function to get card length
int card_length(long cNo)
{
int count = 0;
while (cNo > 0)
{
count += 1;
cNo /= 10;
}
return count;
}

//lacno is Luhn_Algo_Card_Number, lacnolen is Luhn_Algo_Card_No_LENgth
void luhn_algo(long lacno, int lacnolen)
{
//Initialize array of name cardElem with elements eq to card length
int cardElem[lacnolen];
// Initialize integer arrayElem equal to card length
int arrayElem = lacnolen;
//counter is the element that is the 2nd from right
int counter = lacnolen - 2;
// ct is the card length
int ct = lacnolen;
//Initialize variable for the sum at the end of luhn alg
int sum;

//Populate array values with card numbers starting from the ones position
while (arrayElem > 0)
{
cardElem[arrayElem - 1] = lacno % 10;
lacno /= 10;
arrayElem--;
}

//Save a variable called firstValue which is the first value of the card, or the 0th value of the array
int firstVal = cardElem[0];

//Implementation of the luhn algorithm
for (int i = counter; i >= 0; i = i - 2)
{
cardElem[i] *= 2;
if (cardElem[i] > 9)
{
int w = cardElem[i] % 10;
cardElem[i] /= 10;
int x = cardElem[i];
cardElem[i] = w + x;
}
}

//Adding up the elements in the overwritten value of the array
for (int j = 0; j < ct; j++)
{
sum = sum + cardElem[j];
}

if (sum % 10 == 0)
{
finalPrint(firstVal);
}
else
{
printf("INVALID\n");
}
}

void finalPrint(int cardDet)
{
if (cardDet == 3)
{
printf("AMEX\n");
}
else if (cardDet == 5)
{
printf("MASTERCARD\n");
}
else if (cardDet == 4)
{
printf("VISA\n");
}
}
``````

I run `make credit && ./credit` and try selected card numbers and it provides expected results. However when I try `check50 cs50/problems/2020/x/credit` this is the result

``````:) credit.c exists
:) credit.c compiles
:( identifies 378282246310005 as AMEX
expected "AMEX\n", not "INVALID\n"
:( identifies 371449635398431 as AMEX
expected "AMEX\n", not "INVALID\n"
:( identifies 5555555555554444 as MASTERCARD
expected "MASTERCARD\n", not "INVALID\n"
:( identifies 5105105105105100 as MASTERCARD
expected "MASTERCARD\n", not "INVALID\n"
:( identifies 4111111111111111 as VISA
expected "VISA\n", not "INVALID\n"
:( identifies 4012888888881881 as VISA
expected "VISA\n", not "INVALID\n"
:) identifies 1234567890 as INVALID
:) identifies 369421438430814 as INVALID
:) identifies 4062901840 as INVALID
:) identifies 5673598276138003 as INVALID
:) identifies 4111111111111113 as INVALID
``````

I have tried to change some of the printf outputs and determined that the `INVALID` that the program outputs in check50 is the one in `luhn_algo`, but I haven't managed to debug further from there.