Usage of \b and \r in C

The characters are exactly as documented - \b equates to a character code of 0x08 and \r equates to 0x0d. The thing that varies is how your OS reacts to those characters. Back when displays were trying to emulate an old teletype those actions were standardized, but they are less useful in modern environments and compatibility is not guaranteed.

The characters will get send just like that to the underlying output device (in your case probably a terminal emulator).

It is up to the terminal's implementation then how those characters get actually displayed. For example, a bell (\a) could trigger a beep sound on some terminals, a flash of the screen on others, or it will be completely ignored. It all depends on how the terminal is configured.