C++ Language question

I have tried to build the following code (NOT generated by app wizard) under VC++ but I encounter linker error. Would you please help me out?
 
// Here are all the code ------------------------------
 
#include <afxwin.h>
 
class box : public CWinApp
{
public:
    box(){}
    BOOL InitInstance();
};
 
BOOL box::InitInstance()
{
    AfxMessageBox("This is a message box.", MB_YESNO|MB_ICONQUESTION);
        return TRUE;
}
 
box theApp;
 
//end ---------------------------------------------
 
The linker errors are :
 
Linking...
nafxcw.lib(thrdcore.obj) : error LNK2001: unresolved external symbol __endthreadex
nafxcw.lib(thrdcore.obj) : error LNK2001: unresolved external symbol __beginthreadex
libc.lib(crt0.obj) : error LNK2001: unresolved external symbol _main
box.exe : fatal error LNK1120: 3 unresolved externals
Error executing link.exe.
box.exe - 4 error(s), 0 warning(s)
 
Thanks a lot.
 
ka ming
 
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