After learning C, It would be really cool to have a Guided-Porject on making your own programing language, ormaybe even just a lexer and parser. It could work for the course and having unittests by after each section/lesson, you say what each synttax is for what ou make, so you could have a unit test that checks teh ouptuyt of a function it inputs, and you say how you definer functions, the keyword for variable definitions ...