Credit card problem: Unable to calculate the sum of entered credit card no

Question

#include <stdio.h>
#include <cs50.h>
int main(void)
{
long creditcardno;
do
{
    creditcardno = get_long("enter");
}
while (creditcardno < 1000000000000 || creditcardno > 9999999999999999);
int i = 0;
long cc = creditcardno;
while (cc > 0)
{
    cc = cc / 10;
    i++;
}
printf("%d", i);

if (i == 14)
printf ("invalid");
return 0;

int sum1 = 0;
int mod1 = 0;
int mm = creditcardno;
do

    {mod1 = mm%10;
    mm = mm/10;
    sum1 = sum1 + mod1;
    }
while (mm > 0);
printf ("sum of the digits is %d", sum1);

}

I could get output as invalid if 14 digit number is entered. But the last chunk of the problem seems not working.

int sum1 = 0;
int mod1 = 0;
int mm = creditcardno;
do

    {mod1 = mm%10;
    mm = mm/10;
    sum1 = sum1 + mod1;
    }
while (mm > 0);
printf ("sum of the digits is %d", sum1);

I intend to get sum of all the digits before moving to the exact requirements of the credit card problem with CS50.

As part of continuing with the problem, now that I can calculate no. of digits of entered credit card, mark as invalid if a 14 digit no. entered, I am facing issue with figuring out first two digits of entered credit card no. I am once again pasting the full code:

#include <stdio.h>
#include <cs50.h>
int main(void)
{
long creditcardno;
do
{
    creditcardno = get_long("enter");
}
while (creditcardno < 1000000000000 || creditcardno > 9999999999999999);
int i = 0;
long cc = creditcardno;
while (cc > 0)
{
    cc = cc / 10;
    i++;
}
printf("%d\n", i);

if (i == 14)
    {
    printf("invalid");
    return 0;
}
int sum1 = 0;
int mod1 = 0;
int sum2 = 0;
int mod2 = 0;
int d1 = 0;
int d2 = 0;
long mm = creditcardno;
do
{
    mod1 = mm%10;
    mm = mm/10;
    sum1 = sum1 + mod1;
    mod2 = (mm %10) * 2;
    mm = mm/10;
    d1 = mod2%10;
    d2 = mod2/10;
    sum2 = sum2 + d1 + d2;
    
}
while (mm > 0);
printf("sum of the digits %d\n", sum1 + 
sum2);

Till the above, it seems the program is working. From here on, help needed.

long firsttwodigits = creditcardno;
do
{
    firsttwodigits = firsttwodigits/10;
}
while (firsttwodigits > 100);
printf("First two digits are%d", 
firsttwodigits);
}

Not getting the program compiled after adding the last chunk. Here is help50 message:

Asking for help...

credit.c:52:39: error: format specifies type 'int' but the argument has type 'long' [-Werror,-Wformat] printf("First two digits are %d", firsttwodigits); ~~ ^~~~~~~~~~~~~~ %ld

Be sure to use the correct format code (e.g., %i for integers, %f for floating-point values, %s for strings, etc.) in your format string on line 52 of credit.c. ~/pset1/ $

I am not sure if to use %i or %d for printf format. Also seen on some tutorials %li. And if this issue that is creating problem in this chunk.

Update: Indeed by replacing %i with %li, the program is displaying the first two digits.

Help regarding the next leg of the problem is on this new thread: Credit problem: Classifying into Amex/Visa/Mastercard

Answer 1

int mm = creditcardno; This should be a long, it is likely overflowing. You can add some printf for mm and mod1 to help you debug it.