Sieve of Eratosthenes in C99

sieve.c

#include <stdio.h>
#include <stdbool.h>
#include <math.h>
#include <string.h>

#define n 100
static bool A[n];

int main() {
  int i, j;
  int upper_bound = (int) ceil(sqrt(n));

  memset(A, true, sizeof(bool) * n);

  for(i = 2; i < upper_bound; i++)
    if(A[i])
      for(j = i*i; j < n; j += i)
        A[j] = false;
  
  for(i = 2; i < n; i++)
    if(A[i])
      printf("%d is prime\n", i);
  return 0;
}