Goldbach's Conjecture

#include <iostream>
#include <cstring>
using namespace std;
const long long N =100000002;
int esPrimo[N];

void criba(long long n){
    for (long long i=0;i<=n;i++) esPrimo[i]=1;

    esPrimo[0]=esPrimo[1]=0;

    for (long long p=2;p<=n;p++){
        if (esPrimo[p])
            for(long long mul=p*p;mul<N;mul+=p) esPrimo[mul]=0;
    }
}

int main(){
    criba(100000001);
    int num;
    while((cin>>num) && (num!=0)){
        int encontrado=0,a=2;
        while(!esPrimo[num-a]){
            a++;
            while(!esPrimo[a]) a++;
        }
        cout<<num<<" = "<<a<<" + "<<(num-a)<<endl;
    }

    return 0;
}