一个关于C++错误的疑惑!

#include "stdafx.h"
#include "iostream"
#include "exception"

using std::exception;
using std::cin;
using std::cout;
using std::endl;

int hmean(int a,int b);

int _tmain(int argc, _TCHAR* argv[])
{
    int  x,y,z;
    cout<<"Enter two numbers :";
    while(cin>>x>>y&& x!=0&&y!=0)
    {
        try
        {
            z = hmean(x,y);
        }
        catch(exception e)
        {
            cout<<e.what()<<endl;
            cout<<"Enter a new pair of numbes: ";
            continue;
        }
        std::cout<<"Harmonic nean of "<<x<<" and "<<y
            <<" is "<<z<<endl;
        cout<<"Entre next set of numbers <0 0to quit>: ";
    }
    return 0;
}


int hmean(int a,int b) throw (exception )
{
    cout<<" 抓不住!~~~~"<<endl;    
    return 2*a*b/(a+b);  //分母为零时会抛异常
}