Prime numbers and ratio

#include<stdio.h>
#include <iostream>

using namespace std;

int main()
{
    int counter = 0;
    int n,i,j;
    printf("Enter n value: ");
    scanf("%d", &n);
    int prime[n+1];

    for(i = 1; i <= n; i++)
    {
        prime[i] = i;
    }

    for(i = 2; i*i <= n; i++)
    {
        if(prime[i] != 0)
        {

            for(j = 2*i; j <=n ; j += i)
                prime[j] = 0;
        }
    }
    printf("Prime numbers are: \n");
    for(i=2; i <= n; i++)
    {
        if(prime[i] != 0)
        {
            printf("%d ",i);
            counter++;
        }
    }

    cout << endl << endl <<"Counter: " << counter << endl;
    cout << "Ratio: " << (double)n/(double)counter;
}