Thread: Improving the following code:

You haven't actually described your task. Instead, you've left it up to us to look up how it's supposed to be done (very few people have this kind of thing memorized). You also haven't specified whether it's UPC-A or UPC-E.

So, here's the rules that I looked up. They are for UPC-A.

Suppose that you want to find the check digit of UPC-A number 72641217542.

From the right to the left, start with odd position, assign the odd/even position to each digit.
Sum all digits in odd position and multiply the result by 3: (7+6+1+1+5+2)*3=66
Sum all digits in even position: (2+4+2+7+4)=19
Sum the results of step three and four: 66+19=85
Divide the result of step four by 10. The check digit is the number which adds the remainder to 10. In our case, divide 85 by 10 we get the remainder 5. The check digit then is the result of 10-5=5. If there is no remainder then the check digit equals zero.

It can be done with less machinery than you've employed.

Code:

#include <stdio.h>
#include <string.h>
#include <ctype.h>
 
int calc_upca_check_digit(const char *upc) {
    const int ExpectedCount = 11;
    int count = 0;           // count of digits found
    int odds = 0, evens = 0; // sums of "odd" and "even" positions
 
    for ( ; *upc; ++upc) {
        if (isspace(*upc)) continue;
        if (!isdigit(*upc)) break;
        if (count % 2 == 0)
            odds  += *upc - '0';
        else
            evens += *upc - '0';
        ++count;
    }
 
    if (count != ExpectedCount)
        return -1;
 
    int sum = odds * 3 + evens;
    return (10 - (sum % 10)) % 10;
}
 
int main() {
    char line[1000];
    printf("Enter a UPCA code: ");
    fgets(line, sizeof line, stdin);
    int check_digit = calc_upca_check_digit(line);
    printf("Check digit is: %d\n", check_digit);
}

The first thing I notice all the warnings that your code generates (such as passing an int* to a size_t* parameter, which is a no-no). I would change all of your size_t's to int's as there is really no point to using size_t here. _itoa is a non-standard function. What compiler are you using?

This

Code:

    if (d_len - temp_len == 0)

is more commonly written as

Code:

    if (d_len == temp_len)

Here's something strange:

Code:

            while (d > 0)
            {
                int d_split = d % 10;
                splited[i] = d_split;
                break;
            }

That's the same as saying this (i.e., there isn't really a loop because of the break):

Code:

            splited[i] = d % 10;

Is splitDigit divided into two parts just to ensure that any unused elements of the split array are 0? Then just use calloc to ensure they are zero from the start.

The function would be more generally useful if it accepted a string and returned the check digit.

Also, main returns int, not void (void is non-standard although allowed by some compilers). And you don't need the backslash at the end of line 73. Literal strings separated by only whitespace are concatenated (and a newline is whitespace).

So, putting some of this into your code yields:

Code:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define GROUP_SIZE 5

/*  (Not needed anymore.)
char* intToCharArray(int n) {
    int sz = snprintf(NULL, 0, "%d", n); // how much space is needed?
    char *str = malloc(sz + 1);          // +1 for null char
    sprintf(str, "%d", n);
    return str;
}
*/

int* splitDigit(int d, int d_len) {
    int* split = calloc(d_len, sizeof *split);
    for (int i = d_len - 1; i >= 0; i--) {
        split[i] = d % 10;
        d /= 10;
    }
    return split;
}

int oddEvenSum(int* arr, int arr_len, int start, int increment) {
    int sum = 0;
    for (int i = start; i < arr_len; i += increment)
        sum += arr[i];
    return sum;
}
 
int calcUpcCheckDigit(const char *upc) {
    int zth, first, second;
    sscanf(upc, "%1d %d %d", &zth, &first, &second);
    int* firstSplit = splitDigit(first, GROUP_SIZE);
    int* secondSplit = splitDigit(second, GROUP_SIZE);
    int temp[11] = {zth};
    for (int i = 1; i < 11; i++) {
        if (i < 6) temp[i] = firstSplit[i - 1];
        else       temp[i] = secondSplit[i - 6];
    }
    free(firstSplit);
    free(secondSplit);
    return 9 - ( (oddEvenSum(temp, 11, 0, 2) * 3
                + oddEvenSum(temp, 11, 1, 2)    ) - 1) % 10;
}

int main() {
    char line[100];
    printf("Enter the 11 digit UPC code in the following format\n"\
        "*** 0 12345 67890 ***\n>>> ");
    fgets(line, sizeof line, stdin);
    int check_digit = calcUpcCheckDigit(line);
    printf("Check digit is: %d\n", check_digit);
}