pset1 credit working only in certain cases

Question

So, this is probably not a good solution of the problem, but I hoped it would at least work, after struggling with it for quite some time. It made me happy to see it worked for the first number I tested (AMEX), however, when I ran the cs50 test, it turned out it works only for certain cases, and I cannot figure out where the problem is.

Also, when I run the program and enter the credit card number, in certain cases it accepts it and displays result as either invalid or the card name, but in other cases it just keeps prompting me for new entry, and I don't see the reason.

I would really appreciate any help...

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

int main(void)
{
   //Prompt the user for credit card number

  long long ccnumber = get_long_long ("Number: ");

  long long sum1=0;
  long long sum2=0;
  long long di=0;
  long long dj=0;
  long long d1=ccnumber%10;
  long long d2=0;


// Sum the digits that won't be multiplied by 2 (every other digit starting from the last one)

  long long number1=ccnumber;
  while (number1>0)
  {
    number1=number1/100;
    di=number1%10;
    sum1+=di;
 }

// Sum every other digit multiplied by 2, starting with the number’s second-to-last digit

long long number2=ccnumber/10;
long long d2temp=(number2%10);

if(d2temp*2>9)
{
    d2=d2temp%10 + (d2temp/10)%10;
}
else
{
    d2=d2temp;
}

while(number2>0)
{
    number2=number2/100;
    di=number2%10;

    if(di*2>9)
{
    dj=(di*2)%10 + (di*2/10)%10;
}
else
{
    dj=di*2;
}

    sum2+=dj;
}


   long long totalsum=sum1+sum2+d1+d2;



 // Check if the card is valid and what type it is if so

if (totalsum%10==0)
{
    if( (ccnumber>=4000000000000 && ccnumber<5000000000000) || (ccnumber>=4000000000000000 && ccnumber<5000000000000000))
    {
        printf("VISA\n");
    }
    else if( (ccnumber>=340000000000000 && ccnumber<350000000000000) || (ccnumber>=370000000000000 && ccnumber<380000000000000))
    {
        printf("AMEX\n");
    }
    else if(ccnumber>=5100000000000000 && ccnumber<5600000000000000)
    {
        printf("MASTERCARD\n");
    }
    else
    {
        printf("INVALID\n");
    }

}

else
{
    printf("INVALID\n");
}




}

Answer 1

The only reason for the behavior of the program that you describe is the function get_long_long, as it is implemented will only accept integers numbers, without any type of character. Are you entering the numbers manually, or maybe you use copy and paste? . If you use copy and paste it is more than possible that you are copying some non-numeric character, and therefore the function get_long_long() is rejecting the entry.