multiple if...else - is case the only solution?

[MsEngineer]

Hi guys,

I need to create a VI with if-else statements. The problem is that there is 5 such cases. Is there any better solution than using nested cases structure?

To be specific, I want to set a certain wait time for a timer for different input frequencies, ie:

if frequency <500 then time = 3000 ms

if 500<= frequency < 1000 then time = 2500 ms

if 1000 <= frequency <5000 then time = 3000 ms

and so on, I will get probably up to ten such ranges.

I would appreciate any idea! 10 nested cases would look rather silly...

[jeanlucpicard · Accepted solution]

you can wire the numeric value directly to the case selector and set a number of ranges (don't forget to set a default case)

http://zone.ni.com/reference/en-XX/help/371361K-01/glang/case_structure/

http://zone.ni.com/reference/en-XX/help/371361K-01/lvhowto/case_selector_values/

[crossrulz · Accepted solution]

The case structure can accept booleans (and error clusters), numbers (integers), strings, and enums to its case selector tunnel.  In your case, a number.  And you can have ranges too.  So your cases will be "..499", "500..1000", etc.

[billko]

I've done something like this if I expected the values to change:

(As shown, this makes the case statement also able to process floating point numbers, but is a little less self-documenting.)

You can also use Boolean Array to Number instead of the 1D Search Array, but I feel my method is a bit easier to understand.  I will often use code that seems more straightforward but less optimized to more clearly show what is happening if I feel the performance hit is negligible.  It is my thought process that creating developer-friendly code helps make it easy to maintain.

[Hooovahh · Accepted solution]

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@billko wrote:

You can also use Boolean Array to Number instead of the 1D Search Array, but I feel my method is a bit easier to understand.  

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If you do use the boolean array to number, changing the radix view on the case structure to be binary helps sort out what case will be called.  But I agree that it still isn't very readable. 

[MsEngineer]

Thanks, it works and looks good!

[altenbach]

Personally, I would just threshold into an array of frequencies and use the correctly rounded output to index into an array of times. No case structure needed. 🙂

[billko]

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@altenbach wrote:

Personally, I would just threshold into an array of frequencies and use the correctly rounded output to index into an array of times. No case structure needed. 🙂

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That's because you don't play fair.  😉

[altenbach]

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@billko wrote:

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@altenbach wrote:

Personally, I would just threshold into an array of frequencies and use the correctly rounded output to index into an array of times. No case structure needed. 🙂

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That's because you don't play fair.  😉

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Fair enough. 😄

Here's how it could look like. Easily expandable by just adding elements to the array constants. No code changes needed and everything visible at all times. (adding cases to a case structure is much more work, hides more and more code, and is also error prone!). Note that the array of frequencies needs to be sorted, of course.

The code might need to be tweaked depending if you want to include the boundaries into the lower or upper range, so modify as needed. Of course boundaries in DBL are not necessarily what you think they are, so be careful)

[billko]

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@altenbach wrote:

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@billko wrote:

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@altenbach wrote:

Personally, I would just threshold into an array of frequencies and use the correctly rounded output to index into an array of times. No case structure needed. 🙂

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That's because you don't play fair.  😉

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Fair enough. 😄

Here's how it could look like. Easily expandable by just adding elements to the array constants. No code changes needed and everything visible at all times. (adding cases to a case structure is much more work, hides more and more code, and is also error prone!). Note that the array of frequencies needs to be sorted, of course.

The code might need to be tweaked depending if you want to include the boundaries into the lower or upper range, so modify as needed. Of course boundaries in DBL are not necessarily what you think they are, so be careful)

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I am ALWAYS learning stuff from you.  Thank you!