Split Window
The source code below shows how to implement a splitter window using plain win32 API. It uses the WM_MOUSEMOVE, WM_LBUTTONDOWN and WM_LBUTTONUP events to resize and move two child edit controls. This example can easily be modified to implement a vertical splitter. The code should compile fine with any windows compiler. Visual C++ users can create an empty win32 application and add the following code to a new .c file.
Source code: splitter.c