Thread: Can anyone explain clearly the logic of this program?

This program checks whether any of the digits in a number entered by the user appear more than once. What I still can't understand is the code inside "if" statement. What's the idea behind that? We get each of the digits at a time, then that digit is used as an index for the array named "digit_seen"... and then digit_seen[digit] = true... It's confusing to me. Can anyone please explain this program clearly??? Thanks a lot.

Code:

#include<stdio.h>
#include<stdbool.h>

int main(void)
{
	bool digit_seen[10] = {false};
   int digit;
   long n;

   printf("Enter a number: ");
   scanf("%ld", &n);

   while(n > 0) {
   	digit = n % 10;
      if(digit_seen[digit])
      	break;
      digit_seen[digit] = true;
      n /= 10;
   }

	if(n > 0)
   	printf("Repeated digit\n");
   else
   	printf("No repeated digit\n");

   return 0;
}

Let's say the first digit is a 3, so digitseen[3]'s value is checked, and it is zero (false). Since we had a 3, we set digitseen[3] to 1 or true.

Now along comes another 3, and again, we check the value of digitseen[3]. Now the value is 1 (true), so we know that we've had a 3 already.

Originally Posted by Adak

Let's say the first digit is a 3, so digitseen[3]'s value is checked, and it is zero (false). Since we had a 3, we set digitseen[3] to 1 or true.

Now along comes another 3, and again, we check the value of digitseen[3]. Now the value is 1 (true), so we know that we've had a 3 already.

Thanks a lot, Ada... That makes sense to me now...