CS320n

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CS320n Visual Programming

• LabVIEW Control Structures

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What We Will Do Today

• Learn about control structures in LabVIEW
• class work working with control structures

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For Loop

• Just like in Alice, execute some code a fixed
  number of times
• In LabVIEW the loop is dragged around the
  components to be executed repeatedly

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For Loop Mechanics
Count terminal. Wire a number to this. Could be
constant orresult of operation
Iteration terminal. Which execution of the loop
is this? Starts at 0, not 1!
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Count value

• Loops cant execute fractional times
• 0, 1, 2, 3, 4
• Try wiring a floating point number to the count
  terminal
• Not an error
• normal rounding

Coercion Dot
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Expected Output?

• how many times does the loop execute?
• what is the first value of the iteration counter?
  the last?
• tough to see
• add time delay

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Slowed down loop
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While loop

• continue executing until while some condition is
  true (or until some condition is false)
• condition can be anything that has a boolean
  output
• output of function or result of a switch or button

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While Loop Stopping Conditions
Stop if true
Continue if true
Right click to change
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While loop

• Pick and display random numbers until a number
  greater than .99 is selected
• Tunnel takes information out of a loop when
  finished

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Shift Registers

• To get information from one iteration of a loop
  to the next shift register are used
• Pick random numbers and add them together until
  the sum exceeds 1000
• How to keep a running total of them sum?

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Does Not Work

• Why not?

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Fix with Shift Register

• right click on loop boundary and choose add
  shift register

Data from last iteration of loop. Give
initial value.
Data to nextiteration of loop
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Completed Version
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Class work

• Create a LabVIEW program that picks random
  numbers
• Pick random numbers until a value greater than
  0.9999 is picked while loop
• Display how many picks it takes to get a result
  greater than 0.9999
• Run the experiment 10,000 times
• What is the average number of picks required?
  use a for loop
• When that is finished add to the program to
  answer these questions
• What were the maximum and minimum number of picks
  required?