#include <stdio.h> #include <cs50.h>
int main(void) {
#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;
}
}
