paxsali's prime generator in C

//
//  main.c
//  PG2
//
//  Created by Alexander on 05.08.13.
//  Copyright (c) 2013 WhiteBarbarian. All rights reserved.
//

#include <stdio.h>
#include <time.h>
#include <math.h>

#define MAX_PRIMES 10000

int count = 0;
int primes[MAX_PRIMES] = {};

int prime(int n) {
    int r1, r2;

    for (int i = 0; i < count; i++) {
        if (primes[i] < 1) {
            return 0;
        } else {
            r1 = pow(n, 0.5) + 1;
            r2 = n % primes[i];

            if (primes[i] <= r1 && r2 == 0) {
                return 0;
            }
        }
    }
    return 1;
}

int main(int argc, const char * argv[])
{
    clock_t start, stop;
    double diff;

    int i = 2;
    int d = 1;
    int nums[4] = {1, 3, 7, 9};

    start = clock();

    while (count < MAX_PRIMES) {
        while (i < 10) {
            if (prime(i)) {
                primes[count] = i;
                count++;
            }
            i++;
        }
        for (int p = 0; p < 4; p++) {
            i = d * 10 + nums[p];
            if (prime(i)) {
                primes[count] = i;
                count++;
            }
        }
        d++;
    }

    stop = clock();
    diff = (stop - start) / (double)CLOCKS_PER_SEC;

    for (int i = 0; i < count; i++) {
        printf("%d: %d\n", i, primes[i]);
    }

    printf("Completed in %f seconds\n", diff);

    return 0;
}