I'd like to buy a C++ book, one that will be used as a useful collection for perhaps ... throughout my programming life

But then I see in Amazon, there are just soooooo MANY of them. I wonder how much a writer can earn for a book he published at $49/item ?

I guess it may be $5/item as what he can get after a purchase is done
If he has 10 sales, he will have $50, but should 10 sales be done in a day ? I doubt there are books that are never sold actually