C and GUI Programming don't get along well. In this video, I used a lesser-known framework for Graphical User Interface (GUI) programming called GTK (as opposed to Java's JavaFX, Python's Tkinter, or C++'s Qt) to design a GUI for a very basic arithmetic calculator. No parsing, no decimals, no advanced functionality -- just a day to learn GUI development in pure C. To be clear, there are actually MANY ways to do GUI design even in just C. I considered using OpenGL or SDL, though those options seemed more tailored for game development, or even the native Windows API. I ultimately chose GTK because of it was a bit simpler than the Windows API and for it's cross-platform compatibility (across Windows, Linux, and Mac). It was really cool seeing how GTK incorporated an Object-Oriented Programming (OOP) framework into pure C. Of course, GTK is also available in other OOP languages, but it was cool seeing how you technically don't need 'classes' this way.