The most coolest thing I did today is "Live Code Editing" that Casey mentioned in Handmade Hero week 5. The basic idea is to make platform independent code be another translation unit, and compile it to a DLL. Then, we can dynamically load it in the Win32 platform code. By doing so, we can change our game code without reopening the executable file at some point.
I might implement the "Loop editing" feature after I got some entities on the screen. Tomorrow, I will start doing some game code. Until then.