[If you're viewing this in monospaced font, such as Courier, the punctuation
marks I use below may not appear on screen as intended.  My apologies.]

There seems to be some confusion about the differences among a hyphen (-), an
en dash (–), and an em dash (—).  A hyphen, the shortest of the three, is used
to connect parts of words (vice-president).  The somewhat longer en dash is
used to connect the beginning and end of a series (1998–2000 or pp. 334–35).
The longest of the three, the em dash, is used to represent breaks of several
different kinds (To be or not to be—that’s a darned good question).
Typewriters only had hyphens, which were used for both hyphens and en dashes,
while em dashes were typically represented in typewriting by two hyphens.
Word processing programs have all three, so there isn't much need these days
to use double hyphens, although the keyboard still has a dedicated key only
for the hyphen.  In WordPerfect, which I use, if you type two hyphens followed
by another character, the program automatically turns the hyphens into an en
dash; if you type three, you get an em dash.

Dick Veit
Department of English
UNCW