for-loop optimization - needed or not?

Question

Do I have to optimize my FOR-loops like below or the compiler will do that for me?

//this is slow, right?
for (int i = 0; i < menuItem.DropDownItems.Count; i++)
{
    ...
}

//this should be much faster right?
for (int i = 0, count = menuItem.DropDownItems.Count; i < count; i++)
{
    ...
}

PS. I bet this was already posted but I haven't found anything, sorry for a possible dup.

PPS. Sorry, I code a lot of JavaScript - where we have to think these kind of optimizations... May seem ridiculous in .net-world.

Answer 1

Well, it depends on how DropDownItems.Count is implemented - but frankly it's likely to be a simple field-backed property... which would make the first code just as fast as the second, but much more readable.

Readability first - then measure performance and micro-optimize only where necessary.

Where possible, prefer a foreach loop to start with though... again, on grounds of readability.

Even if you do want to use a temporary variable, I would keep the for loop itself simple, hoising the count out to separate variable. Admittedly it means a wider scope, but it's simpler:

int count = menuItem.DropDownItems.Count;
for (int i = 0; i < count; i++)
{
    ...
}

That much is just personal preference though.