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Selection structures are created by dragging these blocks into the center pane in order to apply them to a particularsprite.

Image 11. selection control structures available in scratch.

Missing image.
Image 11. Selection control structures available in Scratch.

How do the two bottom blocks differ?

The bottom block in Image 11 is used to select between two specific actions. The middle block is used when there is only one action and you need to decidewhether to take that action or not. That is the case in this program. If the basketball is touching a beach ball, a specific action is required.If the basketball is not touching a beach ball, no specific action is required.

Specifying the condition on which the decision will be based

Note the empty darker depressed area in each of the blocks shown in Image 11 (the rectangle with the pointed ends) . In order to use either of these blocks, you must drop another block having the same shape into the depressedarea. The block that you drop into that area must specify the condition that will be used to make the decision.

Two groups of programming blocks have the correct shape

Unless I missed seeing some others, there are only two buttons at the top left of Image 4 that expose blocks having the required shape:

  • Sensing (light blue)
  • Operators (green)

In this case, we will select and use a block from the light blue Sensing group. (We will use programming blocks from the green Operators group in a future module.) All of the blocks belonging to the Sensing group are shown in Image 12 .

Image 12. programming blocks belonging to the sensing group.

Missing image.
Image 12. Programming blocks belonging to the Sensing group.

Will use the touching block

We will use the block labeled touching followed by a pull-down list and a question mark.

The items that appear in the pull-down list depend on the sprites that have been added to the program. Forthis program, that list consists of the following choices when the basketball has been selected for programming:

  • mouse-pointer
  • edge
  • LeftBeachball
  • RightBeachball

The top two choices are always there. The remaining choices depend on the sprites that have been added to the program at the point in time when youpull down the list and the sprite that has been selected for programming. (Note that the Basketball sprite does not appear in the above list because it was selected for programming when I examined the list. In otherwords, you can't determine that the basketball is touching the basketball.)

Go back and examine the script

Getting back to the bottom script in Image 8 , you can see that I dragged two copies of the if block shown in Image 11 into the center panel and connected the blocks as shown in Image 8 . Then I dragged two copies of the touching block from the Sensing group shown in Image 12 , and dropped each of those blocks into the corresponding locations in the if blocks in Image 8 .

Then I selected RightBeachball from the pull-down list for one of the touching blocks and selected LeftBeachball from the pull-down list for the other touching block.

Conditions have been established - need actions

At this point, I had the conditions for the two selection structures established, but I hadn't yet specified the actions to be taken when one or theother of the conditions is found to be true.

Questions & Answers

Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
what school?
biomolecules are e building blocks of every organics and inorganic materials.
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
sciencedirect big data base
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
characteristics of micro business
for teaching engĺish at school how nano technology help us
Do somebody tell me a best nano engineering book for beginners?
s. Reply
there is no specific books for beginners but there is book called principle of nanotechnology
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
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.
what is the actual application of fullerenes nowadays?
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.
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
is Bucky paper clear?
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
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.
Do you know which machine is used to that process?
how to fabricate graphene ink ?
for screen printed electrodes ?
What is lattice structure?
s. Reply
of graphene you mean?
or in general
in general
Graphene has a hexagonal structure
On having this app for quite a bit time, Haven't realised there's a chat room in it.
what is biological synthesis of nanoparticles
Sanket Reply
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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Source:  OpenStax, Teaching beginners to code. OpenStax CNX. May 27, 2013 Download for free at http://cnx.org/content/col11498/1.20
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