Primes using sieve method

/* sieve.c - It prompts the user to enter an integer N. It prints out
*           It prints out all the primes up to N included.
*           It uses a sieve method. As primes are found they are
*           stored in an array PRIMES and used as possible factors
*           for the next potential prime.
*/

#include <stdio.h>

#define NPRIMES  1000
#define FALSE 0
#define TRUE  1


int main(void) {
int n;
int i,j;
int flag;
int primes[NPRIMES]; /*It will contain the primes smaller than n
*that we have already encountered*/
int level;           /*1+Number of primes currently in PRIMES*/

/*Introduction*/
printf("Enter value of N > ");
scanf("%d",&n);
level = 0;

/*Main body*/
for(i=2;i<=n;i++) {
for(j = 0, flag = TRUE; j<level && flag; j++)
flag = (i%primes[j]);
if (flag) { /*I is a prime */
printf("%12d\n", i);
if (level < NPRIMES)
primes[level++] = i;
}
}
}