Well what you want to see sounds more like a tutorial than an actual application (I think applications like Notepad++ will be a lot to dive into in the beginning). Since you don't mention any environment you want to program in, you could check out the QT Text Editor Demo. QT is a cross platform GUI Toolkit so you are not bound to a specific operating system but probably harder to setup then a Visual Studio environment in Windows.
For Windows only you might want to think about digging more into the .NET platform (e.g. C#) as suggested in this question. It doesn't help learning C++ but it makes GUI development a hell of a lot easier.
