/* Computes a Universal Product Code check digit */
/* A UPC has twelve-digits, like this:
   0  37000 00407 3
   The last digit is a "check digit" to verify the first
   eleven were read properly.
   Compute the check digit as follows:
   Add together digits 1, 3, 5, 7, 9, 11.
   Add together digits 2, 4, 6, 8, 10.
   Multiply the first sum by 3 and add it to the second sum.
   Subtract 1 from the total.
   Compute the remainder when divided by 10.
   Subtract the remainder from 9.
*/
#include <stdio.h>

int main(void)
{
  int d, i1, i2, i3, i4, i5, j1, j2, j3, j4, j5,
      first_sum, second_sum, total;
  int result;

  printf("Enter the first (single) digit: ");
  scanf("%1d", &d);

  printf("Enter first group of five digits: ");
  scanf("%1d%1d%1d%1d%1d", &i1, &i2, &i3, &i4, &i5);

  printf("Enter second group of five digits: ");
  scanf("%1d%1d%1d%1d%1d", &j1, &j2, &j3, &j4, &j5);

  first_sum = d + i2 + i4 + j1 + j3 + j5;
  second_sum = i1 + i3 + i5 + j2 + j4;
  total = 3 * first_sum + second_sum;

  result =  9 - ((total - 1) % 10);
  printf("The computed check digit is: %d\n", result);

  return 0;
}