Factoring Large Numbers

#include<bits/stdc++.h>
#define mx 1000005

using namespace std;

vector<long long>prime;

bool check[mx];

void sieve()
{
    long long sz,i,j;

    prime.push_back(2);

    for(i=3; i<mx; i+=2)
    {
        if(check[i]==false)
        {
            check[i] = true;

            prime.push_back(i);

            for(j=i*i; j<mx; j+=i+i)
            {
                check[j] = true;
            }
        }
    }
}

int main()
{

    sieve();

    long long n,i,j,len;

    while(scanf("%lld",&n)==1)
    {
        if(n<0)
            break;

        bool tag = false;

        if(n!=1)
        {
            len = prime.size();

            for(i=0; i<len; i++)
            {
                if(n%prime[i]==0)
                {
                    while(n%prime[i]==0)
                    {
                        tag = true;

                        n/=prime[i];

                        printf("    %lld\n",prime[i]);
                    }
                }
            }
        }

        if(n!=1)
        {
            printf("    %lld\n",n);
        }

        printf("\n");
    }

    return 0;
}