Transcript Lecture Notes

CS320n –Visual Programming
More LabVIEW Control Structures
What We Will Do Today
• Learn about other LabVIEW control
structures
Visual Programming
LabVIEW Control Structures
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Case Structures
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•
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conditional execution
like a if – else in Alice or other languages
2 or more sub diagrams
the diagram that executes is based on the
input of a selector
• Selector can be boolean, numeric, or a
string
Visual Programming
LabVIEW Control Structures
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Case Structure
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LabVIEW Control Structures
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Case Structure
Current Case Sub Diagram. Can only view one case at a time.
Selector input.
Will change
based on data
type of input:
boolean, numeric
String
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LabVIEW Control Structures
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Case Structure Example
• Create an instrument
that can convert
degrees F to degrees
C or degrees C to
degrees F
• Must choose which
conversion to make
• use a switch on front
panel to select which
conversion to perform
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LabVIEW Control Structures
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Block Diagram
Choose sub diagram by clicking on increment / decrement arrows
or clicking on the down arrow and selecting from the menu.
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LabVIEW Control Structures
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Use Sub VIs
• Add the C to F and F to C
sub VIs to the block
diagram
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LabVIEW Control Structures
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Partial Block Diagram
Problems with tunnels. If data comes out from one case outputs a value, all
cases must have an output for that value. Not the same for input
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LabVIEW Control Structures
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Completed Block Diagram
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LabVIEW Control Structures
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Completed Front Panel
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LabVIEW Control Structures
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One More Thing…
• Any way to make instrument more user
friendly than input label of “Temp In” and
output label of “Converted Temp”?
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LabVIEW Control Structures
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Different Selectors
• In example selector was boolean
– only two cases, true or false
• selector can be numeric or string
• control for numeric selector can be any
numeric type but will get converted to int
• for string and numeric selector many
possible cases
• right click on selector to add cases
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LabVIEW Control Structures
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Select Function
• simple alternative to if-else
type case structure
• a boolean input
• if boolean is true pass on
the value wired to t
• if boolean is false pass on
the value wired to f
• can handle other data
types
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LabVIEW Control Structures
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Sequence Structure
• In LabVIEW, execution is driven by data
flow
• when the input data is ready, functions
execute
• sometimes no way of telling which order
things will execute
• in most programming languages, flow of
control is not driven by data, but is
sequential based on order of statements in
program
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LabVIEW Control Structures
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Sequence Structure
Flat Sequence structure with 2 more
frames added.
Frames execute in order.
Alternative to Flat Sequence Structure is a
Stacked Sequence Structure.
Visually different in that only one frame visible at a time,
but functionally
equivalent.
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LabVIEW Control Structures
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Class work
• This exercise makes use of loops, but
does not require case structures.
• Monte Carlo method for determining Pi
• pi is the ratio of the circumference of a
circle to its diameter, no matter which
circle you use to compute it.
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LabVIEW Control Structures
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Monte Carlo method
• imagine a quarter of a
unit circle.
(radius = 1)
• pick points at random
– random value of x and y,
between 0 and 1
• use distance formula to
determine if point is
inside or outside circle
1,1
0,1
. outside
. inside
y
– square root of (x^2 + y^2)
• tally up points inside
circle
• pick lot of points
• estimate of pi = 4 *
(points inside / total
number of points)
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LabVIEW Control Structures
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1,0
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Class work
• write a LabVIEW program that picks
random points to estimate pi.
• Allow control for number of random points
to pick
• display resulting estimate of pi
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LabVIEW Control Structures
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