writing gui wrappers for command line tools
 

say for instance i wanted to write a gui for something like telnet. Would I write to stdin, after calling exec on telnet?

Thanks

http://www.ecst.csuchico.edu/~beej/guide/ipc/

Specifically, look at fork() and pipes.

or, you could use tcl/TK and expect.
which is a combination purpose - built for such things.