C implementation of the Sieve of Eratosthenes, an algorithm to calculate prime numbers.

psieve.c

/*
 * Implementation of the sieve of Eratosthenes for finding all the primes up to
 * a given number (MAX in this case).
 * From the command line:
 *   Step 1 (compile): gcc psieve.c -o psieve
 *   Step 2 (run):     ./psieve
 */
#include <stdio.h>
#include <math.h>

#define MAX 1000000

    int main() {
  /* Create an array of values, where '1' indicates that a number is prime.
   * Start by assuming all numbers are prime by setting them to 1.
   */
  char primes[MAX];
  for (int i=0; i<MAX; i++) {
    primes[i] = 1;
  }

  /* Loop through a portion of the array (up to the square root of MAX). If
   * it's a prime, ensure all multiples of it are set to zero (false), as they
   * clearly cannot be prime.
   */
  int limit = sqrt(MAX) + 1;
  for (int i=2; i<limit; i++) {
    if (primes[i-1]) {
      for (int j=i*i; j<=MAX; j+=i) {
        primes[j-1] = 0;
      }
    }
  }

  /* Output the results */
  int count = 0;
  for (int i=2; i<=MAX; i++) {
    if (primes[i-1]) {
      printf("%d\n", i);
      count++;
    }
  }
  printf("There were %d primes up to %d", count, MAX);

  return 0;
}

do you happen to know why 29-30 cause a segmentation fault?