Question

I would like to ask how I can create a scroll bar (slider) in WinApi32 C so I can
send serial port data depending on the position of the thumb in the scroll bar.

Answer 1

You can create a window with a scroll bar by adding the WS_HSCROLL and/or WS_VSCROLL styles to your CreateWindow() call.

hWnd = CreateWindow("YourWnd","Name", 
  WS_OVERLAPPEDWINDOW | WS_HSCROLL | WS_VSCROLL,
  CW_USEDEFAULT, CW_USEDEFAULT, 500, 250,
  NULL,NULL,            
  hInstance,NULL
);

You can then check the location by calling the GetScrollPos() or GetScrollInfo() function.

See MSDN documentation here for more info.