can't believe so many people are arguing against this honestly. you don't mix them in the sense the author means. I take it these people didn't read the paragraphs this was the 'takeaway' from.

For example, the primary reason for the sentence seems to be from the text: "Many code examples in this book won't even compile on a c++ compiler, So we should not mix sources of both languages".

It's not at all about the ability to use c libraries in c++ projects or vice versa :S.... c'mon guys!