IF Statement vs Select Case Statement

Hi 930913,

Each Case or calculation is exactly the same, with a different variable. However, everything builds on that variable, so I can't really set up too many "pre-calculated" values - that's what makes it slow-er than I'd like it to be.

Fulano

Hi 930913, actually, I take that back...each case is a slightly bit different, but I'd say that they are all about 80% similar.

Fulano

x Mod 10
will return 0-10 depending what x is (5>0, 24>2, 59>5, etc)
Could you make one calculation for each case using this as a variable?

Hi 930913,

>>x Mod 10 - will return 0-10 depending what x is (5>0, 24>2, 59>5, etc)
Could you make one calculation for each case using this as a variable?<<

hhhmm....I guess I could if I knew how it works. What is it called? (simply "Mod")

Can you give me a simple example of how you would use it? Let say my equation was something like: 3x +2 = y.

(5>0, 24>2, 59>5, 2>4)
So, if I did something like "x Mod 4", would my equation be:

    3(2)+2 = y ; thus y = 8

Yes,... no,... maybe....

Also, how do you declare all that?

Thanks,
Fulano

Hi 930913,

Here's something interesting...(which I should have tested in the first place).

I conducted a test - the same code - the same number of calculations, where the only difference was performing the logic with an IF statements vs a Select Case Statements. Below are the results:

Using IF Statements:
---------------------------------------------
Start Time: 11/5/2009 12:45:03 AM
End Time  : 11/5/2009 12:45:36 AM
Time Elapsed :  32.859375 (Seconds)   or  0.54765625 (Minutes)====================================================

Using Select Case Statements:
--------------------------------------------
Start Time: 11/5/2009 12:43:17 AM
End Time  : 11/5/2009 12:43:50 AM
Time Elapsed :  32.9375 (Seconds)   or  0.548958333333333 (Minutes)
====================================================

Its close, but the IF Statement is faster by about a thousands of a minute.  It's a lot closer than I expected it to be and maybe not worth the trouble to recode.

I'm not sure why this is....do you have any ideas?

Thanks,
Fulano

Both If and Case work by evaluating the expression to either true or false so there should not be much difference in the performance.

Hmmm. Try it a few times and take an average.
Also, take a look at this site: http://www.aivosto.com/vbtips/vbtips.html#optimize

Gentlemen, thanks for the input. -- Here is another test of a set of calculations that is about 15 times the amount of the original test above. This test took approximately an hour, but CodeCruiser is correct (as usual) in saying that the times will be very close indeed. The difference is about 27 seconds.

In this case however, the Select Case outpaced the IF Statement (not by much), but it did.

Using IF Statements:
---------------------------------------------
Start Time: 11/5/2009 10:31:59 PM
End Time  : 11/5/2009 11:30:48 PM
Time Elapsed :  3528.671875 (Seconds)   or  58.8111979166667 (Minutes)
====================================================

Using Select Case Statements:
--------------------------------------------
Start Time: 11/5/2009 8:08:36 PM
End Time  : 11/5/2009 9:06:58 PM
Time Elapsed :  3501.765625 (Seconds)   or  58.3627604166667 (Minutes)
====================================================

Quite interesting...now the question really becomes, why use one over the other if the speed (which is how I'm measuring efficiency) is not the prime factor? -- Anyone wish to opine?

Thanks,
Fulano

I would hazard a guess that it is for user readability. Lots of if else statements could get confusing.

Aha! If you use big expressions in multiple if statements, it will need to execute it each time whereas it only needs to evaluate it once in a select case.

>whereas it only needs to evaluate it once in a select case.

How about
            Dim T As Integer
            Select Case T
                Case (T < A + B) And (T > B + C)

                Case (T > B + C) And (T < C + A)

            End Select

???

Gentlemen, sorry for the delay. I got sidetracked onto something else.

I think this was an interesting debate and I appreciate your help. In the end, I went with the Case Statement for sake of clarity.

Thanks again,
Fulano