Hold last value on unconnected tunnel in case structure

[hydzik]

I have a true/false case structure as below. I am using it to run some code when an input is true. False condition is empty.

after performing some calcs I tunnel the value out, I wish the false condition to hold the same value, 

how do I achieve this?

Use default if unwired returns a 0 value which I don't want.

Thanks

[crossrulz]

Use a feedback node or a shift register to hold the value.  The value from the FB Node can then go into the structure.  In the false case, just wire up the input and output tunnels.

[hydzik]

Can you please further explain.

The while loop is only available in the true case, the false case is empty.

where do I create the shift register?

[ghighuphu]

You create a shift register on the case structure.

[crossrulz · Accepted solution]

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hydzik wrote:where do I create the shift register?

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I assume that this is running inside of another loop.  You would put the shift register on the loop.  If not, then use a feedback node.

[aputman]

Why not just use a local variable in the false case?

[GerdW]

Hi aputman,

in LabVIEW you trust the DATAFLOW! And the wire is the variable!

So shift registers (or feedback nodes) are the preferred way to store data from one iteration to the next.

Local variables create data copies (as they don't follow the DATAFLOW) and are prone to race conditions…

[JÞB]

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@aputman wrote:

Why not just use a local variable in the false case?

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Let me go ahead and answer that: There are a few reasons:

1. Data Copy.  The Local read makes a copy of the data
2. UI Thread switch. the FBN does not require the use of the UI Thread
3. Initialization options.  the indicator may not have the desired default value or initialize correctly while the FBN can init on each call or on first call
4. What other code exists? you could introduce an unexpected race condition if a local write exists elsewhere.

The FBN is the preferable change 

[aputman]

I understand dataflow just fine.  However i didn't know that FBN could be used outside of loops.  Makes sense now.