A simple question about if then (else) loops.

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Are there any benefits or drawbacks in doing this :

VB

If colmod1 = new_colmod1 Then Else If colmod1 > new_colmod1 Then colmod1 -= 0.001 If colmod1 < new_colmod1 Then colmod1 += 0.001 End If

Rather than doing this? :

VB

If colmod1 <> new_colmod1 Then If colmod1 > new_colmod1 Then colmod1 -= 0.001 If colmod1 < new_colmod1 Then colmod1 += 0.001 End If

Does it compile down to the same code? should I avoid it because?

What I have tried:

N/A..Just for background info and what peoples opinions are.

Posted 22-Sep-17 9:18am

5everin

Updated 26-Sep-17 7:46am

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5everin 22-Sep-17 15:28pm

Ps.
In this particular example the code performs a lot of these tests which will mostly find the values match. Its looking for exceptions in a large dataset.

4 solutions

Solution 3

Better question. Why are you testing to see if the value is "greater than" and then in the next statement testing to see if the value is "less than"?

If the value is not equal, you only need one other if statement to get the two outcomes.

VB

If colmod1 <> new_colmod1 Then
    If colmod1 > new_colmod1 Then 
        colmod1 -= 0.001
    Else
        colmod1 += 0.001
    End If
End If

Posted 22-Sep-17 10:20am

Dave Kreskowiak

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5everin 22-Sep-17 16:29pm

less typing for the example :)

Dave Kreskowiak 22-Sep-17 16:56pm

Also less readable and less performant as an if statement is not a fast operation.

Richard Deeming 26-Sep-17 14:10pm

The code within the If block modifies one of the variables being tested, so it's theoretically possible for the code to execute both blocks. :)

Eg:
colmod1 = 42
new_colmod1 = 41.9991

Dave Kreskowiak 26-Sep-17 17:29pm

True. I saw that but it didn't even occur to me.
The overlying equal/notEqual, greaterThan, lessThan pattern is what stuck in my mind.

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OriginalGriff · Accepted Answer · 2017-09-22T09:27:00

Solution 1

The first one is ugly, and harder to read: there should be no performance difference once optimisation is completed.

Posted 22-Sep-17 9:27am

OriginalGriff

Comments

5everin 22-Sep-17 16:12pm

Thanks, best practice wasn't really what I was after though I understand why you added it in the answer.

CPallini · Accepted Answer · 2017-09-22T09:45:00

Solution 2

They are (visual) basically the same. You might choose the first form just to upset Griff.

Posted 22-Sep-17 9:45am

CPallini

Comments

OriginalGriff 22-Sep-17 16:14pm

:laugh: +5

5everin · Accepted Answer · 2017-09-26T07:46:00

I did a little testing using the stopwatch and 1,000,000,000 iterations of the condition repeated 10 times for each version.

And to answer my own question:

The "nice" soloution is marginally faster than the "ugly" one when the condition always fails. The difference is only only about 1% or less but it seems to be fairly consistent over a few runs.

I guess the Else is more expensive to process.

The "ugly" form seems to be a little faster when the condition is always met by a slighty larger margin maybe 1-2%.

However once the compiler optimisations are turned on in VS. The difference disapears. So indeed there appears to be no reason to use it other than the annoyance factor :)

A simple question about if then (else) loops.

4 solutions

Solution 1

Solution 2

Solution 3

Solution 4

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