Sieve of Eratosthenes

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

int n = 1000000;
int array[1000000];

void sieve()
{
    int i , j , k;
    int sqr = sqrt(n);
    for(i = 4; i <= n; i += 2)
        array[i] = 1;

    array[0] = array[1] = 1;

    for(i = 3; i <= sqr; i += 2)
    {
        if(array[i] == 0)
        {
            for(j = i * 3; j <= n; j += i + i)
            {
                array[j] = 1;
            }
        }
    }
}

int main()
{
    sieve();
    int i , j ,k;
    int num;

    while(~scanf("%d", &num))
    {
        if(array[num] == 0)
            printf("Prime\n");
        else
            printf("Not Prime\n");
    }

    return 0;
}