sieve of eratosthenes prime number

#include <stdio.h>
int main (void)
{
    printf("SIEVE OF ERATOSTHENES ALGORITHM\n");

    int num;
    printf("Give a number: ");
    scanf("%i", &num);
    printf("\nTo Display All Prime Numbers Between 1 and %i\n", num);

    int P[num];

    // initialize array to all zeros
    for (int i = 2; i < num; i++){
        P[i] = 0;
    }

    int i = 2;
    while(i < num){
        // 0 value indicates it is not marked as prime
        if (P[i] == 0){
            printf("%i ", i);
        }
        // set multiples of i to 1
        for (int j = 1; i * j <= num; j++){
            P[i*j] = 1;
        }
        // increment for next number to test
        i++;
    }

    return 0;
}