Which is Faster and Why?

[Arc]

I already know the Answer but i am just curious to see how well known this fact is about the VB compiler.

If i write this code 2 different ways which will be faster once it's compiled?


A)

If iConditionOne < 1 Then
  If iConditionTwo < 20 Then 
      'DoSomething
  End if
End if

B)

If iConditionOne < 1 And iConditionTwo < 20 Then 'DoSomething

[jcfowl]

The first because it evaluates one at a time?????
just a guess.

[Lord_Rat]

Without actually KNOWING the answer, I would say the first.

The second has three evaluations to perform, whereas the first only has two.

[mstic]

B is quicker.

Using method A, VB has to ... dunno if right word " Re-Itterate " Each entry...

It has to trigger the first value before it even looks at the second one....


Method B already states the the 2 values together to look for.. whatever..

I'm right arent i? Just cant explain it very well

[Lord_Rat]

Me thought is such:

Case A

Eval First
Its true
Eval Second
Its true
. . Do processing

Eval First
Its False
Skip over

Case B

Eval First
Its true
Eval Second
Its true
Eval true and true
Its true
. . Do processing

Eval First
Its False
Eval Second
Its True
Eval true and false
Its False
Skip over

[kleinma]

i would say it doesn't matter unless you have some really complex statements... i don't think you would ever see a difference using the example you put up.. even though i am sure it was just an example... the computer is too fast for you to see any difference.. even an old computer... but you know what i am saying right?

[JoshT]

I say A as well, as VB6 does not support short-circuiting, IIRC.

[mstic]

My version of thought was:

Method A:

Search through Everything for First Value
If true Record value and continue to end
Search Through Everything for Second Value
Result

Method B:

Search through Everything for First And Second value near-Simaltoneously


no?

[James Stanich]

A is. Somewhere i read it take more time for VB to evaluate with "and" ... even though it's still eval 2 values.

[mstic]

fine :P

I conceed

it's Eh

[Arc]

JoshT got it correct.

A is faster becasue VB does not use Short Circuiting.

Short Circuiting means that if ConditionOne evaluates to false then it doesnt even look at the rest of the code. But VB however, does look at the rest of the code on that line.

This example alone would not make any difference in overall speed of a project. But if you make a habbit of using Optimization techniques such as this throughout an entire project you will indeed notice a difference.

[Michael_Kamen]

That's correct. We've learned at school that the use of nested if statements can increase speed very much! (Not to mistake it for nested loops, which decreases speed exponently (is that correct?))

[kleinma]

so what does he win???

[Lord_Rat]

Originally posted by Michael_Kamen
That's correct. We've learned at school that the use of nested if statements can increase speed very much! (Not to mistake it for nested loops, which decreases speed exponently (is that correct?))

Not really. It's just that you can end up doing many, many loops, which take a while.

[Michael_Kamen]

Originally posted by kleinma
so what does he win???

Option A

But i think you will find it hard to measure any difference, until you're going to use this kind of statements hundreds of times.