/*
 * Prints all primes <= limit, where limit is an argument.
 * This uses the Sieve of Eratosthenes method.
 */

#include <stdio.h>
#include <stdlib.h>
#define NUM_PER_LINE 10

typedef char bool;

void sieve(bool isPrime[], int m) {
    int n, j, temp;
    for (n = 2; n <= m; n++)
        isPrime[n] = 1;
    for (n = 2; n * n <= m; n++) {
        if (isPrime[n]) {
/* This for loop is a better way to do it than the while loop. */
/*
            for (k = n+n; k <= m; k += n)
                isPrime[k] = 0;
*/
            j = 2;
            while (1) {
                temp = j * n;
                if (temp <= m) {
                    isPrime[temp] = 0;
                    j++;
                } else
                    break;
            }
        }
    }
}

void printPrimes(bool *isPrime, int limit) {
    int n, count = 0;

    for (n = 2; n <= limit; n++) {
        if (isPrime[n]) {
            printf("%8d", n);
            if (++count == NUM_PER_LINE) {
                putchar('\n');
                count = 0;
            }
        }
    }
    if (count > 0) putchar('\n');
}

int main(int argc, char **argv) {
    int limit = atoi(argv[1]);

    /* bool isPrime[limit]; */
    bool *isPrime = (bool *) malloc((limit+1) * sizeof(bool));

    sieve(isPrime, limit);
    printPrimes(isPrime, limit);

    return 0;
}