So I know this is a frequent question, but I still can't find a good one.
It's a 3-week internship where I get to teach high school students. I would cover basic c++ first week, and start the project second week.
What I need is a project that is doable (for them) in 2 weeks. It is interesting. Somehow I want it to be interactive (something that's cool, something that we get to use a lot or something like that)?
Any idea?
Tic-Tac-Toe would be an interesting and fun project. Could start with making the basic game and then moving up to making a computer player.
One of my first class projects was writing a fractal explorer, the instructor had written a simple wrapper class to a windowing/drawing library and basically left it up to us to translate a simple fractal formula into the drawing routine. Depending on how quickly we got it we could add interactive features like zooming, panning, different color palettes, etc.
This project was fun because the end-result was impressive to behold and it allowed the students to explore some aspects of CS (algorithms, visualization, UI) without getting bogged down in too many details of language syntax, windowing libraries, etc.
I'd do hangman. Teaches them very basic text input, ASCII art, and simple text processing. Repetition and iteration over arrays is covered in making sure that when they pick a letter that it covers ALL cases of the letter in the word, and not just one. But it's also very straightforward for somebody who is NOT new to plan out and divide into "easy" pieces IMO.
Very doable in two weeks IMO.
BFS, DFS, Dijkstra, Queues, Stacks, Lists, Trees, MaxFlow problem is good for biginers.
I take it that your Students don't have an extensive knowledge of programming. So why not go for a simple text adventure or quiz type of game where you can cover the basics like conditions and loops?
I'm assuming they only know console stuff, so what they could easily do is a console RPG game, a console Tic-Tac-Toe, minesweeper, hangman, the nim game if you want to go into a bit of math as well, a calculator, a binary clock, a card game simulation. There is a lot. If they know GUI stuff as well, some of these are even better fits.
There are also more algorithm-oriented problems: maze solvers, sudoku solvers etc.
I suggest you give them a list of recommendations and let them choose, maybe even come up with their own ideas. Do you want them to all have the same project? That seems kind of boring, and they might (read: will) copy each other's work. I think each one having a different project that they chose (even if from a list given by you) is better.
Ask them to write a data management console application on windows. All they need to do is delete files in a directory if the disk space falls below a threshold value. From this they will also understand some operating system functions.
Quite honestly, if all you have is 3 weeks and assuming these students have very little to no programming experience (assuming an average high school student), C++ is the wrong language to use.
You could arguably end up spending those entire 3 weeks helping students debug compiler and linker errors just due the difference between declaring a defining a function.
Honestly, if you want beginning students to walk away from a 3 week course, I think you'd be better off choosing a language better suited for it, such as python or even basic. 3 weeks of C++ with no other exposure will likely do nothing but frustrate and turn these students away from the discipline.