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

int main(void) {

long long cc;

//get user input for cc
do
{
    cc = get_long_long("Number: ");

} while (cc <= 0);

//check if cc length is 13, 15, 16

long long num = cc;
int digits = 1;

do
{
    num /= 10;
    digits++;
} while (num >= 10);

 if (digits != 13 && digits != 15 && digits != 16)
{
    printf("Invaild number\n");
    return 1;
}

//check if cc is legit according to Luhn's Algorithm

int number[digits], even[digits];
int i, sum = 0;

for (i = 0; i < digits; i++)
{
    number[i] = cc % 10;
    cc /= 10;

    if (i % 2 == 1)
    {
        even[i] = number[i];
        even[i] *= 2;
    }
    if (even[i] >= 10)
    {
        even[i+1] = even[i] / 10;
        even[i] = even[i] % 10;
    }

    sum += even[i];

    if (i % 2 == 0)
    {
        sum += number[i];
    }

}

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

else
{
    //check if cc is 15 digits starting with 34, 37
    if (digits == 15 && number[14] == 3 && (number[13] == 4 || number[13] == 7))
    {
        printf("AMEX\n");
    }

    //check if cc is 16 digits starting with 51, 52, 53, 54, 55
    if (digits == 16 && number[15] == 5 && (number[14] == 1 || number[14] == 2 || number[14] == 3 || number[14] == 4 || number[14] == 5))
    {
        printf("MASTERCARD\n");
    }

    //check if cc is 13 or 16 digits starting with 4
    if ((digits == 13 && number[12] == 4) || (digits == 16 && number[15] == 4))
    {
        printf("VISA\n");
    }
}

return 0;

}

Hi I can't figure out the problem of my code because debug50 runs fine... It says INVALID and then when I debug it says AMEX. same for VISA. what would be the problem?? Thanks in advance!