Why am I getting an infinite loop?

Question

My output prints positive or negative repeatedly. Why am I getting an infinite loop? I used the following:

include iostream 
using namespace std; 

int main()
{
    int num;

    cout<<"enter number"<<endl;
    cin>>num;

    while(num!=0)
    {
        if(num>0)
            cout<<"positive"<<endl;
        else
            cout<<"negative"<<endl;
    }

    return 0;
}

Answer 1

Based on madflame991's answere here is an improved version :)

include iostream 
using namespace std; 

int main()
{
    int num;

    do
    {
        cout<<"enter number"<<endl;
        cin>>num;

        if(num>0)
            cout<<"positive"<<endl;
        else
            cout<<"negative"<<endl;
    }while(num!=0);

    return 0;
}