[求助]帮忙看看这个程序

//clock
#include<iostream.h>
class Time
{public:
Time()
{hour=0;
minute=0;
second=0;
}
void set_time();
void show_time();
private:
int hour;
int minute;
int second;
};
void Time::set_time ()
{cin>>hour;
cin>>minute;
cin>>second;
}
void Time::show_time ()
{cout<<hour<<":"<<minute<<":"<<second<<endl;
}

int main()
{
Time t1;
t1.set_time();
t1.show_time();
Time t2;
t2.show_time();
return 0;
}
帮忙看看这个程序怎么老是出现error LNK2001: unresolved external symbol _WinMain@16错误