Example Solution:

Modulus Operator and Control Flow Assignment

(Console version)

Which version of C#/ Visual Studio is required for this assignment?
The provided files are (obviously) C#, and (less obviously:) ) they were built using the Visual Studio 2005 product. If you have an older version of Visual Studio (or are using Mono), you probaby won't be able to open the Solution (.SLN) file. If this is the case, in order to build this, you'll need to add all the .CS files to a new project, and then everything should compile & run just fine.
Refactoring / function decomposition
The user-interface input validation can serve as a good example about how bad it is to duplicate code - verbose, easy to miss typos, and inelegant. Wouldn't you rather figure it out once, and then not worry about it anymore? Don't you wish you had functions/methods?
If they have seen methods, it might be a nice add-on for the project to make the student refactor this code, so that there are a couple of routines that can take a (string) prompt, and min & max value, and then call instead of the vast amounts of nearly-identical code that's all in Main.
If you do go that route, it might be interesting to have them discuss / think about how there's a trade-off around specific messages & generalized, reusable code, since they'll probably have to write a validation routine that won't be able to explain that value X is reserved. But again, all of this is beyond the scope of the standard assignment
Student solution - redundant code
Especially since the students have seen a large amount of code duplication in the provided example, they may duplicate a lot of code trying to offer the user three separate operators to be quizzed on. You should be aware of this, and either avoid the problem entirely (for example, remove the non-modulus operators, so that there is only 1 operator) , accept it (if you want to focus the assignment on just the operators), or else head it off early by talking about it in-class, so that they know to look for (and try to factor) out common code
Possible Additional Topic: Random Number Generation
It's easy enough to omit the lines that randomly generate the two operands, if you want the students to also learn Random number generation.