So your program only deals with alpha characters A, B, C, x, y, z ?
Are you aware there is are built in functions toupper and tolower, or was that part of the assignment?
To check for whitespace such as spaces, tabs, newlines etc find out their ascii codes like you have done in the convSpecial function.
With the convPunct function, why the translation of the chars to something else?
If you really want to cheat, read this:
It is really old, and for the C language, but still a good reference I think. You should be aware they are many different ways of doing things in C++. Newbies quite often write C programs with some cout statements, not realising that it would be done quite differently in C++.
Good Luck !!!