I think you have already solved this problem. You just need to think harder and tinker more with it.
In C you can easily display any ASCII character in Dec form.
Here is the ASCII Table for reference.
For example
char c = 65;
char c = 'A'; // Both are the same thing.
So it is probably the same as generating a random number between 65 and 90. Hope this helps ;) Am also new to C with some background in C++.