Multiple Conditions & "is not in"

[deeverd]

Hello LC Forum,

Although for years I've been using if-then-else statements with multiple conditions, with varying degrees of success I might add, it was only yesterday that I thought about reading the documentation for "if." It came as quite a surprise then to discover that an if-then-else should be used only with single conditions, while switch & case should be used for multiple conditions. Apparently it pays to read the dictionary.

Here's my current quandary after hours of experiments:

Multiple conditions with "case" seem to be only about what is true. But what about what's false?

In other words, I find that when I need to set a condition to verify that a portion of a line in a field contains what I am really looking for, I use tVariable "is not in" the field as much as I use fld "Field" contains... In fact, most of the time when I am using multiple conditions, I find that to really isolate the correct portion of a text, I need to use both true and false conditions in conjunction with each other.

So, how can I use an "is not in" with multiple conditions through a switch/case statement?

As an example:

case "tDinosaur"
case "tBrontosaurus"
case not "tRex"

I'm not actually building a dinosaur program, I just like that tRex is the original temporary variable, but I really am hoping that there's a way to accomplish this task that I have been unable to find in the documentation.

Cheers,
deeverd

[dunbarx]

Hi.

It is a matter of personal style which way you do this. That said, "switch" constructions are generally far more easily read, modified and written than "if-then". The inherent structure of switch usually subsumes the nesting required for multiple levels of "if then".

That said, you just need a little practice:

Code: Select all

switch
  case foo = 42
    UltimateAnswer
    break
  case 42 is not in the clipboardData
    answerLiesSomewhereElse
    break
  case ultimateQuestion()
    relaxAndGoWithIt
    break
end switch

Now the other way to do this is:

Code: Select all

put random(99) into foo
switch foo
  case 9
    doThis
    break
  case 2
    snakeEyes
    break
  case 125
    thisWillNeverFire
    break
end switch

You will find that switch usually requires no nested structures at all, though included switch or "if-then" are supported to any level as long as they are all valid LC constructs. But for most purposes, the gadget is just fine, single-level, as per the above. I found this one of the best enhancements coming from HC.

Craig Newman

[SparkOut]

Each "case" contains a block of code that will be enacted if the case resolves to true.
Which means that it is perfectly feasible to resolve a negative case to true.
Eg
switch
case tRex is not tApatosaur
answer "These are not the same"
break
case tRex is not "herbivore"
answer "This is a meat eater"
break
end switch

Edit: slow, slow forum posting by phone.

[deeverd]

Hello Craig and SparkOut,

I had no idea that "is not" could be used in Switch & Case. That will certainly make life a lot easier knowing this info.

Thank you both very much.
All the best,
Allen

[deeverd]

Just realized after playing with the examples of the provided switch & case script that a main part of what I'm trying to figure out is still unclear to me...

To illustrate, here's some clunky code that definitely doesn't work but hopefully it illustrates what I'm after:

Code: Select all

on mouseUp
   switch
      case field "htmlField" contains "<b> "
      case "<i>" is not in field "htmlField"
      case field "htmlField" contains "<u> "
         beep 5	
         break
   end switch
end mouseUp

What I'm trying to do is to figure out, such as in the example above, how to make it beep 5 only if all three conditions are true. In other words, it should only beep 5 if the field contains "<b>" and contains "<u>" and does not contain "<i>"

So all three conditions have to be met at the same time to cause it to beep 5.

Is that possible?

Allen

[SparkOut]

case field "htmlField" contains "<b>" and field "htmlField" contains "<u>" and "<i>" is not in field "htmlField"

If need be, enclose each test within ( )

[SparkOut]

For clarity, each case test is a check to see if the condition being tested resolves to a boolean value of true. Conditions can be strung together with and and or, as per any other boolean tests.

[dunbarx]

Note that if you string cases together in a list, if any of them are satisfied, that case will fire. In other words:

Code: Select all

on mouseUp
   put "true" into y
   switch
      case x or y or z
         answer "Bingo"
   end switch
end mouseUp

is the same as:

Code: Select all

on mouseUp
   put "true" into y
   switch
      case x
      case y
      case z
         answer "Bingo"
   end switch
end mouseUp

Sparkout gave a different, er, case, when he said, essentially:

case x and y and z

Here all have to be true.

Craig

[dunbarx]

Deeverd.

I had no idea that "is not" could be used in Switch & Case.

All valid LC constructs can be used in all valid LC constructs. Sometimes you have to pay attention to the case where LC will evaluate expressions before, say, passing parameters to other handlers. But this is for later...

Craig

[deeverd]

Didn't get a chance to say that between the combination of both your advice, I am finally able to efficiently use multiple conditions including "contained" and "is not in" at the same time. That was a great help. It never dawned on me that using multiple conditions was a simple as placing them all on the same case line like this:

Code: Select all

on mouseUp
   switch
      case ((field "htmlField" contains "<b>") and (field "htmlField" contains "<u>") and ("<i>" is not in field "htmlField"))
         beep 5	
         break
   end switch
end mouseUp

I also tried using commas, semicolons, etc., all in experimentation, but as suggested, found out that good old parentheses and "and" was what worked.

You would think I was a complete newbie, but another surprising thing I hadn't realized was that boolean syntax works perfectly with LiveCode. Surprisingly, although I use "and" on a regular basis, I hadn't realized that I could also use "or"

It's nice to keep learning... even if it is a little embarrassing admitting what I didn't know sometimes.

Thanks so much for all your help.
Cheers,
Allen