EET 2259 Unit 5
Loops
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Read Bishop, Sections 5.1 and 5.2.
Lab #5 and Homework #5 due next
week.
Exam #1 next week.
Floyd, Digital Fundamentals, 10th ed
Structures
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Structures control the flow of a program’s
execution.
This week we look at two kinds:
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For Loops
While Loops
Later we’ll look at other kinds:
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Sequence Structures
Case Structures
…
Floyd, Digital Fundamentals, 10th ed
(Bishop, p. 213)
For Loop
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A For Loop executes the code inside its
borders a specified number of times.
The code inside the For Loop’s borders is
called a subdiagram.
A For Loop has two terminals: the count
terminal and the iteration terminal.
(Bishop, p. 214)
Floyd, Digital Fundamentals, 10th ed
For Loop Example
Floyd, Digital Fundamentals, 10th ed
Placing a For Loop
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For Loops are found on the Functions>>
Programming>> Structures palette.
Click it, and then drag to create a loop on
the block diagram.
Then place items inside the loop to build
your subdiagram.
(Bishop, p. 214)
Floyd, Digital Fundamentals, 10th ed
Be Careful to Place Items Inside the
Loop
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If you’re not careful, you can end up
with items “hovering” over a loop
instead of being located inside the
loop.
Correctly located
inside
Floyd, Digital Fundamentals,
10th edthe loop.
Not inside the loop, but
hovering over it.
Count Terminal
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A For Loop’s Count Terminal, labeled N,
lets you set how many times the loop will
execute.
You can set the count to a constant, or to a
value set by the user through a control, or to
the output of a function, etc.
The count is available to be used inside the
loop.
(Bishop, p. 214)
Floyd, Digital Fundamentals, 10th ed
Iteration Terminal
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A For Loop’s Iteration Terminal, labeled i,
contains the number of loop iterations that
have been completed.
The iteration number is available to be
used inside the loop.
It starts at 0 and increases to N-1.
(Bishop, p. 214)
Floyd, Digital Fundamentals, 10th ed
Inserting a Time Delay
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Loops usually run so quickly that the user
can’t see what’s happening.
To add a time delay, use either the oldfashioned Wait (ms) function or the newer
Time Delay Express VI.
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Both are found on the Functions>>
Programming >>Timing palette.
Place either one anywhere inside the loop.
Floyd, Digital Fundamentals, 10th ed
Good Practice: Include a Time Delay
in All Loops
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What if you don’t want to slow down the
loop to “human speed,” but want it to run as
fast as possible?
It’s still a good programming practice to
include a small (10 ms) delay in your loop.
This prevents LabVIEW from consuming all
of your processor’s time, and lets the
operating system perform necessary tasks.
Floyd, Digital Fundamentals, 10th ed
Tunnels
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If a wire crosses the border of a loop (or
other structure), a tunnel automatically
appears on the border.
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Doing this can be useful, but can also lead
to confusion unless you keep in mind the
following point….
Floyd, Digital Fundamentals, 10th ed
Tunnels and Data Flow
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No data passes into or out of a structure
while the structure is executing.
Input data is read before the structure
executes; subsequent changes to the input
values are ignored.
Output data is not available until after the
structure finishes executing.
Floyd, Digital Fundamentals, 10th ed
Example For Loop in BASIC
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The type of loop we’ve been discussing is
called a “For Loop” because in text-based
programming languages (such as BASIC
or C++) it is coded using the word FOR.
Example:
CLS
FOR i = 1 TO 15
PRINT i, 2 * i
NEXT i
Floyd, Digital Fundamentals, 10th ed
Integer Representations
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Recall that blue terminals and blue wires
represent integers.
Integer terminals can be further categorized
into byte signed integer (I8), word signed
integer (I16), long signed integer (I32), etc.
This is called the “representation” of the
number, and you can change it by rightclicking on a terminal and choosing
“Representation.”
Floyd, Digital Fundamentals, 10th ed
Integer Representations (Continued)
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These representations differ in the range of
values they can handle and the amount of
memory they use.
Representation
Max. Value
Memory Bytes
Byte signed integer (I8)
127
1
Word signed integer (I16)
32,767
2
Long signed integer (I32)
2,147,483,647
4
Quad signed integer (I64)
 11019
8
Byte unsigned integer (U8)
255
1
Word unsigned integer (U16)
65,535
2
Long unsigned integer (U32)
4,294,967,295
4
Quad unsigned integer (U64)
 2 1019
8
Floyd, Digital Fundamentals,
10th
ed
Floating-Point Representations
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Recall that orange terminals and orange
wires represent floating–point numbers.
Floating-point terminals can be further
categorized into single precision, double
precision, and extended precision.
Floyd, Digital Fundamentals, 10th ed
Floating-Point Representations
(Continued)
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These representations differ in the range of
values they can handle and the amount of
memory they use.
Representation
Max. Value
Memory Bytes
Single-precision (SGL)
 3.40 x 1038
4
Double-precision (DBL)
 1.79 x 10308
8
Extended-precision (EXT)
 1.19 x 104932
16
Floyd, Digital Fundamentals, 10th ed
Coercion Dots
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If you wire together two terminals of different
numeric representations, LabVIEW must
convert the number from one representation
to the other.
In these cases a red dot called a coercion
dot will appear on the terminal where the
conversion takes place.
Coercion dots are bad. They waste
memory, and can lead to rounding errors that
are difficult to find.
Floyd, Digital Fundamentals, 10 ed
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th
(Bishop, p. 216)
Numeric Conversion Functions
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LabVIEW has functions for converting a
number of any representation to any other
representation. (For example, the To Word
Integer function converts any number to the
I16 representation.)
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These functions are found on the Functions
> Numeric > Conversion palette.
These are sometimes useful in eliminating
coercion dots.
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Floyd, Digital Fundamentals, 10th ed
While Loop
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A While Loop executes the code inside its
borders repeatedly until a certain condition
is met.
A While Loop has two terminals: the
iteration terminal and the conditional
terminal.
(Bishop, p. 221)
Floyd, Digital Fundamentals, 10th ed
While Loop Example
Floyd, Digital Fundamentals, 10th ed
Placing a While Loop


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While Loops are found on the Functions
>> Programming>> Structures palette.
Click it, and then drag to create a loop on
the block diagram.
Then place items inside the loop to build
your subdiagram.
Floyd, Digital Fundamentals, 10th ed
Iteration Terminal
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A While Loop’s Iteration Terminal, labeled
i, contains the number of loop iterations
that have been completed.
It behaves just like a For Loop’s iteration
terminal.
The iteration number is available to be
used inside the loop.
(Bishop, p. 221)
Floyd, Digital Fundamentals, 10th ed
Conditional Terminal
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A While Loop’s Conditional Terminal
determines at the end of each loop execution
whether the loop will be executed again.
You set the Conditional Terminal to either
Stop if True or Continue if True.
Usually you’ll wire a Boolean control or the
output of a Boolean function to this terminal.
(Bishop, p. 221)
Floyd, Digital Fundamentals, 10th ed
Conditional Terminal:
Stop if True
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When the Conditional Terminal is set to
Stop if True, it looks like a red stop sign on
the block diagram.
A true condition will cause the loop to stop
executing, but a false condition will cause it
to execute again.
(Bishop, p. 221)
Floyd, Digital Fundamentals, 10th ed
Conditional Terminal:
Continue if True
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When the Conditional Terminal is set to
Continue if True, it looks like a green
looping arrow on the block diagram.
A true condition will cause the loop to
execute again, but a false condition will
cause it to stop executing.
(Bishop, p. 221)
Floyd, Digital Fundamentals, 10th ed
Example While Loop in BASIC
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This type of loop is called a “While Loop”
because in text-based programming
languages it is coded using the word WHILE.
Example:
CLS
INPUT “Guess my age. ”, guess
WHILE guess <> 46
INPUT “No. Try again. ”, guess
WEND
PRINT “You got it!”
Floyd, Digital Fundamentals, 10th ed
For Loop With a Conditional
Terminal
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It’s possible to add a conditional terminal to a
For Loop, creating a loop that behaves like a
cross between a For Loop and a While Loop.
To do this, right-click a For Loop’s border
and select Conditional Terminal.
(Bishop, p.220)
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We won’t use this feature in this course:
Whenever I refer to a For Loop, I mean a
plain For Loop without a conditional terminal.
Floyd, Digital Fundamentals, 10th ed