switch怎么用,我的怎么错

#include<iostream.h>
void main()
{
switch(msg)
{
case WM_COMMAND:
switch(wJParam)
{
case IDM_F_NEW:
delete wfile;
wfile=new WinAppFile;
break;
case IDM_F_OPEN:
wfile->FileOpenDlg();
break;
}
case WM_CREATE:
break;
case WM_PAINT:
break;
default:
return DEFWindowProc(hWnd,Message,wParam,LParam);
}
}