* thwaps IR *
Bad, bad!
Use the cctype header instead of ctype.h - the former is a C++ library, and the latter is a C library. The only difference is that in the C++ version, everything is in the std namespace. As IR points out, this library contains a number of functions designed to do exactly what you want to do: isalpha checks whether the character passed to it is a letter, for example.
For punctuation, you'll have to check 'em manually:
switch (character)
{
case '.':
case '?':
[...]
// do stuff
break;
}