the Oblivion ConstructionSet Wiki

Talk:If

Revision as of 19:54, 20 November 2008 by imported>Relax and Play (Request for else/elseif)

Do brackets help in logical operations?

IE: elseif Random > 75 && ( LilRandom == 4 || LilRandom2 == 4 )

That should be if Random is over 75, and LilRandom or LilRandom2 equals 4, but what I gather is that Oblivion will interpret it as:

if Random is over 75 and LilRandom is equal to 4, OR LilRandom equals 4.

Logically it should interpret it the prior, but with Oblivion, I'm not so sure. --MaXiMiUS 21:42, 9 April 2006 (EDT)


--JOG 15:21, 14 April 2006 (EDT)Doesn't help as far as I've tested it.

--JOG 04:51, 17 April 2006 (EDT) Didn't really read and thought you asked about AND/OR as bitwise operators. Of course brackets work but since OR always has priority over AND you need to include the AND part.

tabs and spaces

I just spent an hour searching for a bug in a script using &&:

Apparently certain combination of tabs and spaces between the two parameters cause the IF-Block to break processing of the script. No commands within the IF-Block or after the IF-Block are executed.


Here is an example:

http://home.tiscali.de/jo.ge1/tabs_working.txt

This one works fine: for each of the three objects you get a Journal entry when you activate it and can activate it as often as you like.


http://home.tiscali.de/jo.ge1/tabs_not_working.txt

The second one doesn't work: You just get the journal entry when you activate the first object, no activation, And the second and third object can't be activated at all.

--JOG 15:27, 14 April 2006 (EDT)

This is verified that the problem in the second script is due to using spaces instead of tabs. To avoid this problem ensure that all operators, numbers, identifiers, and brackets in expressions have a space on each side of them. -- Daveh 19:24, 22 September 2006 (EDT)
Actually you need to use the same separator on each side (either space or tab) and seperators are only necessary for a minus operator to differentiate it from a negative sign. The first example script uses 07 & & 07 and the second one 07 & & 20--JOG 03:27, 23 September 2006 (EDT)

Gotchas

The following if condition compiled (I forgot to type the last angleA): 

if (angleA >= 0 && angleA <= 90) || (angleA >= 180 && < 270)

Once my script hit this line, it stopped working completely. No indication that anything was wrong. --Mrflippy 21:06, 15 April 2006 (EDT)

That's a CS "Gotcha", but a "normal" behaviour in regards to OB's engine: you have 2 operators following each other, "&& <", without their required right or left operands. Although the CS "compiler" itself does not seem to have the required verification functionality in this regard (from what you are saying), thus letting you package a mod with a blatant error, it will bug when playing the game. --HawkFest 17:58, 26 May 2008 (EDT)
In Oblivion modding we often refer to any kind of silent failure as a "Gotcha" - you get absolutely no indication of what's wrong, it just doesn't work. You don't know if its your code or just some stupid error like this. It's very frustrating, so having a list of these kinds of things is important.
There are a number of these... we have a list somewhere. I need to find that so we can make it more noticeable.
Dragoon Wraith TALK 18:09, 26 May 2008 (EDT)

Also,

Sometimes a runtime error will occur where: 

      if cond1 && cond2
         ;code
      endif

is not evaluated correctly in scripts. If you find a similar conditional statement is not functioning correctly, try: 

      if cond1
         if cond2
            ;code
         endif
      endif

The reason for this anomaly is currently unknown.

A confusing text

The paragraph about Combining comparisons: « Note that "||" is evaluated before "&&", just like "*" is evaluated before "+" in normal algebra. » is a confusing argument, and should give an explanation for a matter of major consequences:

  • In arithmetic and algebra, from the earliest use of mathematical notation, multiplication took precedence over addition. The standard order of operators is: 1-exponents and roots; 2-multiplication and division; 3-addition and subtraction.
  • In terms of computing, we're talking about precedence here. The precedence is a number order, and operator precedence is usually ordered with the corresponding number order. For expressions where two operators of different precedences compete for the same operand, the operator with the higher precedence wins.
  • In Common operator notation, involving "normal" alegebra or boolean algebra, "*" is evaluated before "+", it has a higher precedence number than the "+" operator. For example, 3×4+5 = ((3×4)+5), not (3×(4+5))

However, from what I've read this is not the case here. It seems that OR has a higher precedence than AND, since the article mentions the following: if myVar1 == 1 && myVar2 == 1 || myVar2 == 5 is equivalent to (if myVar1 == 1 && (myVar2 == 1 || myVar2 == 5)). Else, we'd have ((if myVar1 == 1 && myVar2 == 1) || myVar2 == 5).

Which explains why one has to be very careful in positioning conditions in a condition list of an editor item: for the CS/OB's engine, OR has order preference, has precedence over AND. For example, the condition items (A AND B OR C AND D) are evaluated as (A AND (B OR C) AND D), and not (( A AND B) OR (C AND D)), as opposed to common operator notation for most languages: we call this an inversed or negative notation. Always keep the later in mind when applying boolean algebra for evaluating some given expression, as standard operator notations will lead you to errors. --HawkFest 17:37, 26 May 2008 (EDT)

OK, I agree with everything you've written, but I'm not exactly clear on what you are suggesting be done with this article. You've described everything very accurately as I know it. What's wrong with the way the article is written, then? It seems to be saying just what you are, to me at least.
Feel free to change the article if you think you can write it better - your explanation here is certainly much more detailed than the article, so if you think the article needs the more detailed explanation, go ahead. As always on the Wiki, be bold - just go ahead and change things when you think there is a problem. Explain what you do on the Talk page, and if people disagree with your edit they can talk about it and we can compromise - it's trivial to undo things in the Wiki if necessary thanks to the History page.
Dragoon Wraith TALK 18:06, 26 May 2008 (EDT)
I found it confusing as the statement is right, but also showed an opposite behaviour which, IMHO, needs to be clarified as it impacts the design of boolean expressions, in terms operators notations for scripting any conditional expressions. Ok, I will modify the article. I just wanted some feedback about my own understanding before doing so: even though it is trivial to modify something in the Wiki, it's not that trivial to detect if the modified article can mislead to some error of understanding from the neophyte reader (until the article actually gets changed), something I wouldn't want to do... Thanks! :) --HawkFest 18:19, 26 May 2008 (EDT)

Testing negative numbers

I had some weird results with 

if (SomeVar >= -1)

but the line worked fine with 

if ((SomeVar + 1) >= 0)

Are negative numbers not handled properly? Do they need to be set to a variable first? Thought I'd seen so on another page, but it's not on this one (where it should be).--Haama 19:04, 8 July 2008 (EDT)

Nested IF's

Can someone explain to me nested IF's and how exactly they differ from using an && operator? I feel this is unclear in the article (I have read the appropriate section multiple times and still find it difficult to understand) and it has produced its fair share of "Gotcha's" in my scripting endeavours. For example: 

 If ( GetItemCount Item1 == 1 ) && ( GetItemCount Item2 == 1 )
  ;Do something here
 endif

How exactly is the above code different from this: 

 If GetItemCount Item1 == 1
  If GetItemCount Item2 == 1
   ;Do something here
 endif
  endif

Except, of course, for the added lines of code. It would seem using the && operator is more effecient but I prefer to use nested IF's as I've found they work for me???--Antares 22:33, 25 August 2008 (EDT)

Logically, they're the same... but logic doesn't work well here...
There are essentially two reasons you'd want to use nested ifs instead of &&s: safety and speed.
  1. Safety - Oblivion will run every test, even if the first test fails. That's not a big deal for your example, but in cases where you need a valid reference (If Ref && (Ref.GetItemCount Item1)) you can easily cause a CTD when the reference is 0.
  2. Speed - It's faster to run two checks on the same line (If... && If...) than to run two if checks, but only when you expect both conditions to be true most of the time. If either one is rare, it'd be faster to use two if checks. Scripts that check for input are a great example of this - the Keychain mod waits for you to press Activate, makes sure you have the Keychain, and then moves the keys over. I could combine the checks into if (GetControlPress 5) && if (player.GetItemCount Keychain), but because Activate is pressed maybe once every 1000 script runs, it'd take less processing to run if (GetControlPress 5), have it return false, and skip the second, if (player.GetItemCount Keychain) check.
--Haama 00:20, 26 August 2008 (EDT)

Else/elseif?

These two commands are not covered here. While I would add a section for the two commands myself, scripting is my current weak point in Oblivion modding. If anyone would, add an entry explaining the functions of else and elseif. --Relax and Play 19:54, 20 November 2008 (EST)

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