Which loop take more time?

Or C#, right? And not for C... I would avoid bravely answering the "question", as others did.
It's enough to say that the question is, strictly speaking, totally pointless.
"for" relies on indexed access, and "foreach" — on IEnumerable, both can be implemented in such a way to screw up all the performance.
Asking for preferences is just ridiculous, and the attempt to "optimize" something (even though it could be possible in each concrete case) just naive.
There is nothing to discuss seriously.
—SA

CPallini 14-May-15 15:47pm

'for' is shorter than 'foreach' hence, it takes less time, at least in spelling it.

Sascha Lefèvre 14-May-15 17:13pm

:-)

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Sascha Lefèvre · Answer 1 · 2015-05-14T07:17:00

I assume you have a typo in your question and meant to ask "Which loop take more time for or foreach?"

Obviously, a for loop is a different thing than a foreach-loop and it's not always (easily) possible to exchange one for the other. In cases where it is easily possible, a for-loop is (usually) slightly faster than a foreach-loop because it (usually) just increments or decrements an integer variable but a foreach-loop requires an enumerator. Depending on what you do inside the loop, the for-loop can have additional performance-benefits.

I would suggest: If your code inside the loop isn't performance-critical use a foreach-loop if possible because it is (IMO) more intuitive to read. Otherwise use a for-loop if possible. And: Don't bother with optimization before you recognize that performance really is an issue.

PIEBALDconsult · Answer 2 · 2015-05-14T08:21:00

Solution 3

" The decrementing for is faster than the incrementing for, which is faster than the foreach. This is often true regardless of what's being iterated.

...

Of primary importance is to always remember and never forget that the readability of foreach comes at the cost of being slower than for -- that really is a 20x difference between the two (yellow and green) techniques.
" -- On why to use DataViews[^]

Posted 14-May-15 8:21am

PIEBALDconsult

Comments

Sergey Alexandrovich Kryukov 14-May-15 17:08pm

You are right in some points, but I would not answer such question at all — please see my comment to the question, in reply to the comment by C Pallini.
—SA

Raul Iloc · Answer 3 · 2015-05-14T07:07:00

Solution 1

You can see the benchmark results about this in the next article:
For Vs Foreach - Benchmark 2013[^]

Posted 14-May-15 7:07am

Raul Iloc

Comments

Sergey Alexandrovich Kryukov 14-May-15 14:37pm

Sorry, you referenced quite a poor article. Please see my comment to it.
The real answer would be: formulation of the question is not correct. Comparison with just two syntactic constructs is pointless. The loop code cannot be the same, and performance can greatly depend on the code. In case of foreach, it depends, for example, on the implementation of IDisposable.
—SA