How would I make my c++ program output something to another programs text box? If that's even possible. I'm making a bot for another program and have no idea how to write to that programs text box through c++
It can be done, but C++ is not the way to go. Use something that has already been intentionally designed to do what you want. For instance, check out AutoHotkey.
If you absolutely insist on using C++ despite it being a bad idea, then you will need to look into your platform's API. If you are on Windows, you need to look into the Windows API to find how to simulate keypresses.
I Google'd "linux simulate key press" and got plenty of good results. Normally I would be more helpful, but I don't like to support language misuse. (and I don't have easy access to linux without a slow VM)