Performance: While-loop

Question

Simple question: What is best, method 1 or method 2?

Is method 2 faster/better:

List<int> data = Enumerable.Range(0, 10000000).ToList();
int j = 0;

// Method 1
while (j < data.Count)
{
    // do something
    j++;
}

j = 0;

// Method 2   
while (j++ < data.Count)
{
    // do something
}

or would a simple for-loop still be better?

Update: according to the comments, a subquestion: Should while-loops be avoided or should for-loops be avoided and replaced with these while-loops?

I do have a feeling, that after jitting & optimization theese two methods will be compiled into the same machine code — undefined, May 14 '12 at 09:17
There IS a difference, but only that `j` in method 2 will be always 1 ahead of `j` in method 2, considering the amount of iterations, when inside the while body. — SimpleVar, May 14 '12 at 09:18
@Peter the only *functional* difference is if `j` is used inside the loop. The other differences; really minimal./ — Marc Gravell, May 14 '12 at 09:18
Frankly, this is actually a `for` loop or `foreach` loop, and should be written as such, or even better: a `foreach` loop over `Enumerable.Range(...)` ***without*** calling `ToList()` — Marc Gravell, May 14 '12 at 09:19
updated the question. so should for-loops be used or just method 1? — juFo, May 14 '12 at 09:36
Strange that this has downvotes but I still get different answers from people. — juFo, May 14 '12 at 09:46
If you're worried about performance, use a for loop over an array. The JIT compiler has special range-check-elimination optimizations for that. It will matter more than little things such as where the increment goes. — harold, May 14 '12 at 10:08

score 2 · Accepted Answer · answered May 14 '12 at 09:47

2

I would suggest neither, rather I would suggest this

List<int> data = Enumerable.Range(0, 10000000).ToList();
int j = -1;



// Method 1   

while (++j < data.Count)
{
    // do something
}

int j = 0;
do
    {
        //anything
    } while (++j<data.count);

pre-increment operation is faster than post, although a small performance advantage

answered May 14 '12 at 09:47

zahreelay

1,742
12
18

Is the "++i is faster than i++" argument still valid? I thought I read somewhere that it wasn't anymore (or I could be wrong???)? – intrigued_66 May 14 '12 at 11:12
@user1107474 I would love to see where you found that. – juFo May 14 '12 at 11:40
@juFo I just did a quick search on stackoverflow and the answer could be language-dependent. I may have seen a post referring to a different language. – intrigued_66 May 14 '12 at 12:42

score 1 · Answer 2 · answered May 14 '12 at 09:17

1

There is no difference (at least significative in terms of performance, you should measure on really heavy calculations)

I would choose the first one, cause it seems clearer, to me.

answered May 14 '12 at 09:17

Tigran

61,654
8
86
123

score -1 · Answer 3 · answered May 14 '12 at 09:19

-1

Both are take same execution time,There is no difference.You can use any of that in your poject.

answered May 14 '12 at 09:19

Shin

280
1
2
11

Performance: While-loop

3 Answers3