arrays - introduce ++ syntax

[ErikSchierboom]

The arrays exercise introduces for loops, and within that for loop the ++ operator is used. However, we haven't introduced the student to the ++ operator. I think it makes sense here to introduce that operator in introduction.md file of the arrays exercise. The after.md document can then mention the different between x++ and ++x and introduce the decrement operator (x-- and --x)

An alternative to the above would be to include the ++ and -- operator in the after.md document of the numbers exercise or possibly even the basics exercise (not my preference).

[mikedamay]

arrays / for-loops sounds like a good place for ++ and --.

[ErikSchierboom]

👍