It actually appears that C-3P0 is the correct
spelling and hyphenation of the name. Artoo Detoo
is written as such, and hyphenated R2-D2
. See Threepio
is written out this way; logically
, following the same hyphenation rules, it would be writen, numerically, as C-3P0
Also, in the novelizations, when it's written numerically, and even on the *official* website, www.starwars.com, it's C-3PO.