When to use For Each...Next vs For...Next

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Two of my Text/Reference books say that it is better to use For Each...Next loops if possible as opposed to For...Next loops. I am using the code shown below. It works fine. What the code does is move partial rows of data (columns 1 through 4 and column 6) from one dgv1 control to another dgv2 control, where column 1 must meet the If criteria. My question is, how would this code look if it used a For Each construct.

VB

For Me.g = 0 To dgv1.RowCount - 1
            If dgv1(0, g).Value = txtClass.Text Then
                dgv2.Rows.Add()
                For Me.h = 1 To 4
                    dgv2(h, j).Value = dgv1(h, g).Value
                Next
                dgv2(6, j).Value = dgv1(6, g).Value
                j = j + 1
            End If
        Next

Posted 3-Jun-15 8:21am

Member 10628309

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Maciej Los · Answer 1 · 2015-06-03T08:42:00

Please, read this article:
FOREACH Vs. FOR (C#)[^]
In .NET, which loop runs faster, 'for' or 'foreach'?[^]

Member 10628309 asked:

how would this code look if it used a For Each construct.

VB

For Me.g = 0 To dgv1.RowCount - 1
            If dgv1(0, g).Value = txtClass.Text Then
                dgv2.Rows.Add()
                For Me.h = 1 To 4
                    dgv2(h, j).Value = dgv1(h, g).Value
                Next
                dgv2(6, j).Value = dgv1(6, g).Value
                j = j + 1
            End If
        Next

for example:

VB

For Each r As DataGridViewRow In DataGridViewRowCollection
    'for loop body
Next

For further information, please see:
For Each... Next statement[^]
DataGridViewRow[^]
DataGridViewCollection[^]

Sergey Alexandrovich Kryukov · Answer 2 · 2015-06-03T08:40:00

Solution 1

This is simple enough. If in each iteration you need index of the element, use "for". If you need to guarantee certain order of operations, use "for". In all other cases, try to use "foreach".

One delicate case is when you need to modify the set you are iterating during iterations, in particular, remove some elements, one approach is: using "for" iterating from high index to low index. Be very careful with such cases. Other, more complicated cases, need special consideration. In such cases, just use you logic.

Remember that exact behavior of "foreach" depends on how the interface System.IEnumerable is implemented, how its implementation of System.Collections.IEnumerator behaves. Please see:
https://msdn.microsoft.com/en-us/library/system.collections.ienumerable%28v=vs.110%29.aspx[^],
https://msdn.microsoft.com/en-us/library/system.collections.ienumerable.getenumerator(v=vs.110).aspx[^],
https://msdn.microsoft.com/en-us/library/system.collections.ienumerator%28v=vs.110%29.aspx[^].

For one thing, it would be wise not to rely on any peculiar features known from a particular implementation of this interface. From the other hand, you can implement this interface in a specific way, to make some extra assumptions valid, but I would not recommend it.

If you want to say: "this answer pretty much says 'it depends', nothing else", this is essentially what it meant to be. :-)

[EDIT]

I later realized that my answer did not address some more specific problems of the question. So, please see Solution 2 and my comment to it.

—SA

Posted 3-Jun-15 8:40am

Sergey Alexandrovich Kryukov

Updated 3-Jun-15 9:26am

v2

Comments

Maciej Los 3-Jun-15 14:50pm

Why someone downvoted it?
This is good answer. +5!

Sergey Alexandrovich Kryukov 3-Jun-15 14:59pm

Thank you, Maciej.

Ha-ha, it looks like some people are fighting over my answers in some weird ways these days. (And this is a hi-rep case.) What would you say, for example, about this funny thing: http://www.codeproject.com/Answers/997285/MS-Web-Development-Which-to-learn-in?? :-)

That would be all right, but it also hurts my favorite "JavaScript Calculator" article. I really think this is one of the most useful, because I tried to dismiss serious misconceptions and because this is my real working tool which could be useful for many. One user even sent me his gratitude on my personal contact.

—SA

Maciej Los 3-Jun-15 15:12pm

Some people misunderstood the way we can help. One of them is to "giving a fish" and the second one is to "giving a fishing rod". Both are acceptable, but everyone knows that the second way is much, much better!

Sergey Alexandrovich Kryukov 3-Jun-15 15:19pm

Set aside teaching how to fish. Apparently some take the attempt to teach them as an offense. Those may not even accept a fish, they will wait until someone fry it and serve on a plate, where they won't eat it anyway... :-(
—SA

Maciej Los 3-Jun-15 15:37pm

What kind of fish do you serve today? :laugh:
I really do like herring with jigger of vodka... Cheers, Sergey! Na zdrowie!

Sergey Alexandrovich Kryukov 3-Jun-15 15:51pm

I have a very interesting post to write on this proverb. I hope you will like it. When I'm done I'll notify you.

Interestingly, In US there is no much herring. Some know this word and fish, some never heard of it. Most of it comes from Russian/Ukrainian/Jewish businesses. But the supply of fish elsewhere and the variety greatly improved during last ears, I guess, mostly due to increasing farming. When I moved here, I was just shocked by extremely scarce choice and high prices. Not a problem right now.

Будем здоровы!

—SA

Maciej Los 3-Jun-15 16:03pm

Let's move our discussion to Skype... ;)

Sergey Alexandrovich Kryukov 3-Jun-15 17:51pm

I don't mind but you are hard to reach. I would enjoy having a conversation.
—SA

Maciej Los 3-Jun-15 17:56pm

I was, let's say: outside ;)
Did you receive my message?

Sergey Alexandrovich Kryukov 3-Jun-15 17:59pm

No; sorry, I'll be able to get to it (if you mean Skype) much later tonight. In worst case, we might be able to contact on weekend, but I'm online every late evening/night and usually in the morning.
—SA

Maciej Los 3-Jun-15 18:04pm

OK, let's try to be in touch on weekend...

Sergey Alexandrovich Kryukov 3-Jun-15 21:04pm

Now, this is my post on teaching fishing I promised to show:
Feeding Apple or Why Don't We Answer Some Questions.

I hope you like my own saying mocking this old proverb. :-)

—SA

Sergey Alexandrovich Kryukov 3-Jun-15 15:09pm

Frankly, the person who down-voted this answer could have some valid reasons.
This person could keep in mind some important consideration which should be taken into account; which I missed or even failed to see. Some may see important performance difference, which I did not even consider.

Only this is one of the cases when a comment would be helpful. (No, I don't say all down-voted on answers should be commented; some don't even deserve a comment, but I hope many my answers do deserve commenting. :-)

—SA

Maciej Los 3-Jun-15 15:30pm

Keeping in mind the past does not help in judging...

CPallini · Answer 3 · 2015-06-03T10:06:00

Solution 3

I think your code is well addressed by the For .. Next loop.
However, I wouldn't have used member variables as loop indices even if my life depended on it.

Posted 3-Jun-15 10:06am

CPallini