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

int main(void)
{
    long long card;
    // variable credit card number
    long long cc_number;
    // variable card number to be used for counter later on
    long long c;
    long long amex = 10 ^ 15;
    long long mastercard = 10 ^ 16;
    long long visa13 = 10 ^ 13;
    long long visa16 = 10 ^ 16;
    int counter;
    int sum1 = 0;
    int sum2 = 0;


    do
    {
        printf ("credit card number:");
        card = get_long_long ();
    }
    while (card < 0 );

   //hey! come and declare variables here later if code dosent work

   // code for sum
   while (cc_number > 0)
   {
       // a represents every other digit multiplied by 2
       int a = ( (cc_number % 100) / 10) * 2;

       // b represents all other digits
       int b = ( (cc_number % 100) / 10) * 2;

       if (a > 9)
       {
           sum1 = sum1 + (a % 10) + 1;
       }

       else
       {
           // sum1 stores the value of the sum of all as'
           sum1 = sum1 + a;
       }

       // sum2 stores the sum of all other digits
        sum2 = sum2 + b;
        cc_number = cc_number / 100;
   }
   // counts digits
    for (counter = 0; c > 0; counter++)
        {
            c = c / 10;
        }
    // adds the previous sums in this code,and must end with 0 to be valid
    int sum = sum1 + sum2;

    // prints visa using the following conditions
    if ( (counter==16 && (sum %10) == 0)  && (card / visa16) == 4 ) || ( (counter == 13 && (sum % 10) ==0 && (card / visa13) == 4) )
        {
            printf ("VISA \n");
        }
    // prints amex using the following conditions
    else if (counter == 15 && (sum % 10) == 0 && (card / (amex) ==34 || card / (amex) == 37)
        {
        printf ("AMEX \n");
        }
    // prints mastercard using the following conditions
    else if (counter == 16 && (sum % 10) == 0 && (card / mastercard > 50 && card / mastercard < 56) )
        {
        printf ("MASTERCARD \n");
        }
    // prints invalid if none of the above conditions is met
    else
    {
        printf ("INVALID \n")
    }
}