How can I do a For loop while increasing n 5 by 5?

I’m trying to do that:

for (var n : int = 0 ; n < theList.Count() ; n + 5) {

}

I want to go through a list of unknown length (a multiple of 5).

But it throws the error: “Expressions in statements must only be executed for their side-effects.”

How do I achieve a 5 by 5 increment?
Thanks

for (var n : int = 0 ; n < 5 ; n += 5) {

}

You must use += when using these statements. n+5 is a statement, not setting the variable. += is a simplified version of n = n + 5;