Uva 583 Prime Factors

/* Find the Prime Numbers using Seieve Eratonthenis. And then find the Prime factorization of your desired number. */

/*
    Uva 583  Prime Factors
    Verdict:: Accepted

*/

#include <iostream>
#include <cstdio>
#include <cstring>
#include <map>
#include <string>
#include <vector>
#include <cmath>
#include <cctype>
#include <sstream>
#include <set>
#include <list>
#include <stack>
#include <queue>
#include <algorithm>
#define sf scanf
#define pf printf
#define sfint scanf ("%d %d",&a,&b)
#define sfl scanf ("%ld %ld",&a,&b)
#define sfll scanf ("%lld %lld",&a,&b)
#define sfd scanf ("%lf %lf",&a,&b)
#define sff scanf ("%f %f",&a,&b)
#define loop(i,n) for(i=0;i<n;i++)
#define LL long long
#define L long
#define nl puts("")
#define MX 1000005
#define N 100
#define MOD 10000000007
#define pb push_back
#define pi acos(-1.0)
#define sz size()
#define gc getchar ()
#define ps push
#define clr clear
#define bn begin()
#define ed end()

using namespace std;

bool flag[MX]; vector<int> p; int plen; vector<int>prf; int pflen;

void prime()
{
    int i,j,qrt;
    flag[0]=flag[1]=true;

    for(i=4;i<=MX;i+=2) flag[i]=true;

    qrt=(int) sqrt(double(MX));

    for(i=3;i<=qrt;i+=2)
    {
        if(!flag[i])
        {
            for(j=i*i;j<=MX;j+=i+i)
            {
                flag[j]=true;
            }
        }
    }

    p.push_back(2);

    for(i=3;i<=MX;i+=2)
    {
        if(!flag[i])
        {
            p.push_back(i);
        }
    }

    plen=p.size();
}

void primefacto(int n)
{
    int i;
    for(i=0;i<plen and p[i]*p[i]<=n;i++)
    {
        if(!(n%p[i]))
        {
            while(!(n%p[i]))
            {
                prf.push_back(p[i]);
                n/=p[i];
                if(n==0 or n==1) break;
            }
        }
    }

     if(n!=1)
        {
            prf.push_back(n);
        }
}

int main()
{
    int n,i,len;

    prime();
    while(sf("%d",&n)==1 and n)
    {
        pf("%d = ",n);  bool f=false;

        if(n<0)
        {
            f=true;
            n=abs(n);
        }

        primefacto(n);

        sort(prf.begin(),prf.end()); pflen=prf.size(); len=pflen;
        //loop(i,pflen) cout << prf[i] << " ";
        if(f) pf("-1 x ");
        //else
        //{
            loop(i,pflen)
            {
                pf("%d",prf[i]);

                if(len>1)
                {
                    pf(" x "); len--;
                }
            } nl;
        //}
        prf.clear();
    }

    return 0;
}