How to solve this problem?

Hello all:
      I want to use my creating interface and in the client I will call
it,Look:
1:I write a idl,the file name is IAdd.idl,
import "oaidl.idl";
import "ocidl.idl";
[
 object,
 uuid(A62A1F29-485B-478E-BE48-9182A42FB76C)
]
interface IAdd : IUnknown
{
 HRESULT Add([in] long n1,[in] long n2,[out,retval] long *pS);
};
and then: midl IAdd.idl, and then it build IAdd.h,IAdd_i.c,
2:I create a COM using atl,and insert new atl object,short name Sub,
and I copy IAdd.h,IAdd_i.c to my project path,and I open the file stdAfx.h,
add two sentence:
#include "IAdd_i.c"
#include "IAdd.h"
3:I open head file and cpp file:
class ATL_NO_VTABLE CSub :
 public CComObjectRootEx<CComSingleThreadModel>,
 public CComCoClass<CSub, &CLSID_Sub>,
 public ISub,
//*****************************************
 public IAdd
//*****************************************
{
BEGIN_COM_MAP(CAdd)
 COM_INTERFACE_ENTRY(ISub)
//**********************************************
 COM_INTERFACE_ENTRY(IAdd)
//**********************************************
END_COM_MAP()
public:
 STDMETHOD(Add)(/*[in]*/ long n1,/*[in]*/ long n2,/*[out,retval]*/long *pS);
};

..CPP:
STDMETHODIMP CMin::Add(long n1, long n2,long *pS)
{
// TODO: Add your implementation code here
*pS=n1+n2;
return S_OK;
}
I compile and it has no error.

4:now I write client codes,
#include <windows.h>
#include <iostream.h>

#include "..\sub\sub.h"
#include "..\sub\sub_i.c"
void main()
{
HRESULT hr;
hr=CoInitialize(NULL);
ISub *pISub=NULL;
hr=CoCreateInstance(CLSID_Sub,NULL,CLSCTX_INPROC_SERVER,IID_ISub,(void**)&pI
Sub);
long res;
hr=pISub->Min(22,10,&res);
IAdd *pIAdd=NULL;
hr=pISub->QueryInterface(IID_IAdd,(void**)&pIAdd);
if(FAILED(hr))
{
cout<<"error"<<endl; //I find the error on this.
}
.....
}
Who could tell me how to solve it?thank you very much.