Looping Additions: Property Nodes and Shift Registers

[SercoSteveB]

Given an initial value of 1 for Numeric Value In; what is the value of Numeric Value Out following execution of the VI?

a) 5

b) 6

c) 7

d) 8

[crossrulz]

D

But just so people know.  If I see you write code like this, I will majorly yell at you in a code review.  Should be using shift registers all the way.

[VSC]

i agree with D. the loop count is 3 thus the loop goes for 0,1,2. and the resultant for number value is =4. therefore when the loop is satisfied the final addition results to 4+4. thus the answer is D.

[MrStevenUND]

ANS: D 

Edit: Steve, You are beeing sneaky.  The answer is E: none ALL of the above/undeterminable.  You have a race condition here....  When does the control-to-addition happen compared to the FOR loop?  I believe most of the time, you'll get A, but this is not guaranteed.

I second crossrulz's comment.  This is a horrible way to code (EDIT: not just the race condition that I didn't initially see).  The sad part is I have seen some code like this on projects I have inherited (EDIT: minus the race condition)...

[SercoSteveB]

What is this international pick on Steve day ?

I hereby promise to use good programming style ; I reserve the right to sometimes deviate a little (or more than a little) to get my point across.  

Question delivery is key.

[nmpundlik]

Ans is A.

[Asha_Nagaraj]

Answer is A.

[crossrulz]

Good call MrSteven.  I fell into the classic "what are they trying to test" instead of thinking it clearly.

[#9]

I am going with answer A.

Maybe I am missing something, but I don't see a race condition MrStevenUND mentions.

[crossrulz]

DavidCorney wrote:

                       

I am going with answer A.

Maybe I am missing something, but I don't see a race condition MrStevenUND mentions.

                   

You don't see the control outside of the FOR loop and the property node writing to it inside of the FOR loop?

[#11]

Are we stating that there is a race condition, because you could modify the control while the loop is running? My bad to assume that the user would not change the control once execution starts (or have time).

As an aside, is anyone else having to log in to the community site every time they open the page?

[crossrulz]

DavidCorney wrote:

                       

Are we stating that there is a race condition, because you could modify the control while the loop is running? My bad to assume that the user would not change the control once execution starts (or have time).

No.  It is a race condition because when will the control terminal be read for the final addition.  It is being read and written to inside of the FOR loop and therefore who knows what value will be read from the terminal when it does decide to read.

[#13]

Okay, got it. I need more coffee. Thanks!

[GayatriT]

Ans is A.

[SercoSteveB]

Answer: A (most likely).   Nice one nmpundlik, Asha_Nagaraj, DavidCorney & GayatriT

Good spot MrStevenUND.  Yep it does contain a race condition, but I prefer to think of it as a Dataflow Paradigm question.  Another one of those little gotchas that is easy to fall into if you are not concentrating (or concentrating more on the coding style eh GM ?)

[adiveppa]

ans is A

[jagadishj]

A is the write answer.

[mini09]

wow wow my first thoght was B later when I try with the code go with A.... Nice one. what are the different race conditions possible in LabVIEW and how do we say it is an race condition.

[LordNobady]

race conditions are mostly possible with writing to variable ( global's and locals ) and writing to property node's when any of them is done watch for race conditions.

other interesting points ( data flow ) are reads from variables, property nodes or front panels. thy can ( and mostly will ) happen as soon as that part of the code is executed.

this is interesting mostly for stop buttons in loops.

if the data can be changed (programaly) before the point the value is required it can give unexpected results. and in a lot of cases can be called a race condition.

[ashwinilele]

Ans is A

[ashwinilele]

Value is read by control then it's node value just like variables . So ans is A

[skian]

A),

This was a great question. I guess the answer is  it is better understood while following the data when highlighting execution is on.