# 1.6 Scr0360: logical operators in scratch 2.0  (Page 3/7)

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The range of each slider variable is set to -10 to 10.

## Event handlers

Three event handlers, shown as the bottom three scripts in the programming panel in Image A , are written to fire each time the button is clicked.

## Program operation

At runtime, the user adjusts the value of each of the slider variables.

When the user clicks the button, each event handler evaluates a relational-logical expression (an expression containing both relational and logical operators) . If the expression evaluates to true, a value of true is displayed in one of the bottom three variables on the stage in Image A . If the expression evaluates to false, a value of false is displayed in thatvariable.

## Meaningful variable names

In an earlier module, I told you that you should always strive to use meaningful variable names. At this point, you are probably thinking thatvariables named A , B , C , and D aren't very meaningful, and if so, your thinking is correct. However, there is a practical reason that I didn't use meaningful variable names in this case.

## Insufficient space

Really meaningful variable names usually require about five or more characters. However, I have limited display width in this presentation format. If I had used longer names for the variables in this program, theexpressions containing those variable names would have been quite long, and would have made it difficult for me to fit Image A into this presentation format.

You will note, however, that the bottom three variable names on the stage in Image A (also see the variables in the Data toolbox in Image A ) are meaningful. In fact they are probably more meaningful than would be thecase in Java because Java doesn't allow the space character, the left angle bracket character, or the "(" character to be included in a variable name.

## A truth table

According to Wikipedia:

"A truth table is a mathematical table used in logic -- specifically in connection withBoolean algebra, boolean functions, and propositional calculus -- to compute the functional values of logical expressions on each of their functionalarguments, that is, on each combination of values taken by their logical variables. In particular, truth tables can be used to tell whether a propositional expression is true for all legitimate input values, that is,logically valid."

## What does this mean?

The concept of a truth table is simpler than the above quotation might suggest. Image B is a simple truth table that shows the result of evaluating four logical expressions for all combinations of the values of two variables, A and B , where each variable can only take on the values of true and false .

## The and operation

If both A and B are true, then the expression (A and B) evaluates to true. Otherwise, it evaluates to false. Correspondingly, if (A and B) is true, then not(A and B) is false. Otherwise, it is true. Applying the not operator to a boolean value is often referred to as getting the complement of that value.

## The inclusive or operation

The operation that I am getting ready to discuss in known as an inclusive or operation. There is also an exclusive or operation that I won't discuss in this module. That will be a topic for a much more advanced module.

Is there any normative that regulates the use of silver nanoparticles?
what king of growth are you checking .?
Renato
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
why we need to study biomolecules, molecular biology in nanotechnology?
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
why?
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
anyone know any internet site where one can find nanotechnology papers?
research.net
kanaga
sciencedirect big data base
Ernesto
Introduction about quantum dots in nanotechnology
what does nano mean?
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
absolutely yes
Daniel
how to know photocatalytic properties of tio2 nanoparticles...what to do now
it is a goid question and i want to know the answer as well
Maciej
Abigail
for teaching engĺish at school how nano technology help us
Anassong
Do somebody tell me a best nano engineering book for beginners?
there is no specific books for beginners but there is book called principle of nanotechnology
NANO
what is fullerene does it is used to make bukky balls
are you nano engineer ?
s.
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
Tarell
what is the actual application of fullerenes nowadays?
Damian
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
Tarell
what is the Synthesis, properties,and applications of carbon nano chemistry
Mostly, they use nano carbon for electronics and for materials to be strengthened.
Virgil
is Bucky paper clear?
CYNTHIA
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
NANO
so some one know about replacing silicon atom with phosphorous in semiconductors device?
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Harper
Do you know which machine is used to that process?
s.
how to fabricate graphene ink ?
for screen printed electrodes ?
SUYASH
What is lattice structure?
of graphene you mean?
Ebrahim
or in general
Ebrahim
in general
s.
Graphene has a hexagonal structure
tahir
On having this app for quite a bit time, Haven't realised there's a chat room in it.
Cied
what is biological synthesis of nanoparticles
how did you get the value of 2000N.What calculations are needed to arrive at it
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