As you can see, I just want to print something, and iostream is added, but that means I cout can’t use it.

hold   If StdAfx. H is placed at the front of the whole file, no error will be reported

In fact, if other header files are mentioned to the front, an error will be reported – this may be the provision of VS2010,   StdAfx. H must be first.

Even if you comment it out   All include in StdAfx. H are commented out. Whether the compilation passes or not.