It depends on what you're doing with the text. In some cases, a double hyphen with surrounding spaces will be automatically converted to a dash, but that might not work with a triple hyphen. If you must enter text in typewriter style, I'd suggest using space and a double-hyphen for a dash.
It is much clearer, however, to use the correct characters, and with the widespread use of UTF-8, these should print correctly on most platforms.
In typography, a dash can be represented either as an en-dash surrounded by a space on each side – like this – or as an em-dash character with no spaces—like this. The en-dash with spaces is sometimes better behaved at line breaks, but the em-dash is arguably more correct. The en-dash is traditionally used mostly for number ranges (eg, 100–114).
These characters can be easily inserted on a Mac keyboard (Option-hyphen and Shift-Option-hyphen). It's more awkward on Windows (Alt-0150 and Alt-0151), but there are many ways to remap the keyboard or use a program substitute other keystrokes for dashes. (AutoHotKey is very good and free.)