Condense a Number (Digital Root) in C

#include <stdio.h>

int condenseNumber(int number) {
    int n = number;
    while (n > 9) {
        int digitSum = 0;
        while (n > 0) {
            digitSum += n % 10;
            n /= 10;
        }
        n = digitSum;
    }
    return n;
}

int main(void) {
    int number = 9875;
    printf("The condensed form of %d is: %d\n", number, condenseNumber(number));
    return 0;
}

#include <stdio.h>

int digitalRootNonnegative(long long n) {
    int r;
    if (n == 0) {
        return 0;
    }
    r = (int)(n % 9);
    return r == 0 ? 9 : r;
}

int main(void) {
    printf("dr(9875) = %d (closed form)\n", digitalRootNonnegative(9875));
    printf("dr(999999999999999999) = %d (closed form)\n",
           digitalRootNonnegative(999999999999999999LL));
    return 0;
}

#include <stdio.h>

#define CHAIN_CAP 32

struct Result {
    int root;
    int chain[CHAIN_CAP];
    int chainLen;
};

struct Result condenseWithChain(int number) {
    struct Result result;
    int n = number;
    int digitSum;

    result.chainLen = 0;
    result.chain[result.chainLen++] = n;

    while (n > 9) {
        digitSum = 0;
        while (n > 0) {
            digitSum += n % 10;
            n /= 10;
        }
        n = digitSum;
        if (result.chainLen < CHAIN_CAP) {
            result.chain[result.chainLen++] = n;
        }
    }
    result.root = n;
    return result;
}

int main(void) {
    struct Result result = condenseWithChain(9875);
    int i;

    for (i = 0; i < result.chainLen; i++) {
        if (i > 0) {
            printf(" -> ");
        }
        printf("%d", result.chain[i]);
    }
    printf("\n");
    printf("Digital root: %d\n", result.root);
    printf("Also: 1 + (9875 - 1) %% 9 = %d\n", 1 + (9875 - 1) % 9);
    return 0;
}