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Comment by dkersten | Hacker News Reader

Won't this.MyControl.TabPages[i] be invalid once i becomes greater than what this.MyControl.TabPages.Count now is? Since the "always remove element 0" code from the article works, I expect your code won't work because when you remove an element form the list, all subsequent elements now have an index one less than before, so after j/2 elements, you'll overrun the list.

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Correct. I think the logical thing to do would be to delete from the end so that the index is always valid.

for (int i=this.MyControl.TabPages.Count - 1; i > 0; i--) { this.MyControl.TabPages.Remove(this.MyControl.TabPages[i]); }

Imagine the count is 2. The first iteration you delete item 1, the second you delete item 0, and then the loop exits.

EDIT: Actually, as someone else pointed out, it's clearer to use a while loop that deletes the 0th item until the collection is empty.

Actually, you will never delete the final element with that code.

I think what you meant was:

for (int i=this.MyControl.TabPages.Count; i > 0; i--) { this.MyControl.TabPages.Remove(this.MyControl.TabPages[i-1]); }

I prefer:

    for (int i=this.MyControl.TabPages.Count - 1; i >= 0; i--)  {
        this.MyControl.TabPages.Remove(this.MyControl.TabPages[i]); 
    }

Though a simple while loop is much easier to follow, even if its less efficient than removing the elements in reverse.

Although your point on efficiency stands (at least with data structures that have to reshuffle contents on deletion), the type of loop that you use has nothing to do with the order that you delete the elements. You could easily do something like:

while (MyControl.TabPages.Count > 0) { MyControl.TabPages.RemoveAt(MyControl.TabPages.Count-1); }

For loop are nothing more than while loops with:

(1) an assignment (int i = MyControl.TabPages.Count in this case)

(2) an extra command (i-- in this case) added to the end

Sure. Though if we're talking about efficiency, I would imagine that counting backwards would be slightly faster than getting the current count each time. Though in reality this depends on way too many factors - I imagine TabPages would be stored in cache and getting the count is just as fast as counting backwards. Micro-optimization and all that.

Regarding for vs while, I find the choice is important only in the intent they emphasize: while puts emphasis on the condition, whereas for puts the emphasis on the iteration. I think in this case the condition (that the list is not empty) is deserves more emphasis than the iteration through the elements of said list - hence why I find the while version to be more readable. YMMV and all that :)

Exactly. For example in JavaScript doing a something.length would result in re-counting the number of elements, while doing the loop in this style would efficiently store the count in a variable that is fast to access and manipulate. I suppose if you want to be a real optimization junky you'd also use --i instead of i--.

I suppose if you want to be a real optimization junky you'd also use --i instead of i--.

Ten years ago, sure, but nowadays I trust the compiler to do this for me ;-)

That's also what I read of it.

It's TFA's method, except broken (or not fixed, word it as you prefer).

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