How to rollback lines from cout?

You can do cout << '\r'; to jump to the beginning of the current line, but moving upwards is system-specific. For Unix, see man termcap and man terminfo (and search for cursor_up). On ANSI-compatible terminals (such as most modern terminals available on Unix), this works to move up: cout << "\e[A";.

Don't try seeking in cout, it's unseekable most of the time (except when redirected to a file).

As mentioned in other answers, using the ncurses (or slang) library provides a good abstraction for terminal I/O on Unix.

Instead of filling with spaces (which is error-prone, because not every terminal is 80 characters wide), you can do \r + clr_eol: std::cout << "\r\e[K" << std::flush.

Use an output formatting library such as ncurses if you can; this simplifies terminal manipulation significantly.