Inputting into another program (C/C++)

So, how do you do it? I'm trying to create a NetHack character generator, but for that I need my program to input text into it in a predetermined way. Everything I read about interprocess/interprogram communication is far too complex for what I need, I'd rather start slowly and then go building up the concepts. Finally, cheating is not my main concern here (changing the source would be much easier), learning is, so don't go crazy because I asked!

>>1
Please, you HAVE to tell us what platform you're running. You wouldn't use the same techniques on Linux as you would on Windows.

Also, if I understand things you want to do something like:

game: What kind of character would you like to create? a) Warrior b) Priest ...
program: a

game: Strength 21 Dexterity 4 Intelligence 5 ... a) OK r) Reroll
program: r

game: Strength 4 Dexterity 10 Intelligence 5 ... a) OK r) Reroll
program: r

...

Is that it?