Sieve of Eratosthenes in C

sieve.c

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

int *simple_sieve(int limit) 
{
    char is_prime[limit + 1];
    memset(is_prime, 1, limit + 1);

    unsigned int count_of_primes = 0;
    for (int n = 2; n <= limit; n++) {
        if (is_prime[n]) {
            count_of_primes += 1;
            for (int m = n * n; m <= limit; m += n)
                is_prime[m] = 0;
        }
    }

    int *primes = (int *)calloc(count_of_primes + 1, sizeof(int));
    unsigned int c = 0;
    for (int n = 2; n <= limit; n++) {
        if (is_prime[n])
            primes[c++] = n;
    }
    primes[c] = 0; // sentinel

    return primes;
}

int main(int argc, char *argv[])
{
    int *primes = simple_sieve(100);

    for (unsigned int i = 0; i < primes[i] != 0; i++)
        printf("%d ", primes[i]);
    printf("\n");

    free(primes);

    return 0;
} 

Re-implemented in C99.