hdu 2161 Primes

#include<iostream>
#include<cstring>
#include<algorithm>
#include<math.h>
using namespace std;
int main()
{
int num[20000];
int k=1;
int n;
int i,j;
memset(num,0,sizeof(num));
for(i=2;i<=sqrt(16000);i++)
{
for(j=2*i;j<=16000;j=j+i)
{
if(num[j]==0)
num[j]=1;
}
}
num[1]=num[2]=1;

while(cin>>n)
{
if(n<=0)
break;
//cout<<num[3]<<endl;
cout<<k<<": ";
if(num
==0)
cout<<"yes"<<endl;
else
cout<<"no"<<endl;
k++;
}
return 0;
}