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The blue block labeled move 90 steps causes the basketball to move 90 steps forward (in the direction that it is facing) . Each step constitutes one unit in the Cartesian coordinate system. For example, if you were to change this value from 90 to 240, thatwould cause the basketball to move from the origin to the extreme right edge of the Stage.

The selection block

As I indicated earlier , the selection structure is sometimes referred to as a decision structure. In other words, this structure causes the program to select or make a decision between two alternatives. The pseudocode in Image 9 describes this process.

Image 9. pseudocode for a selection structure.

if a specified condition is true perform a specified actionotherwise (when the specified condition is not true) perform a different action
Image 9. Pseudocode for a selection structure.

Sometimes the second part of the selection process isn't needed. In other words, in some cases, if the specified condition is not true, there is norequirement to do anything at all. That is the case in this program.

Two independent decisions

This program makes two independent decisions shown by the pseudocode in Image 10 .

Image 10. two independent decisions.

if the basketball is touching the beachball on the right turn around and face to the leftif the basketball is touching the beachball on the left turn around and face to the right
Image 10. Two independent decisions.

These two decisions are implemented by the two light tan blocks in Image 8 containing the word if . (From this point forward, I won't distinguish between dark tan and light tan.)

Clicking the tan Control button shown at the upper center in Image 4 exposes a large number of programming blocks. Twoof them are used to create pure selection structures (if-then and if-then-else) and one is used to create a combination of a loop structure and a selection structure (repeat-until).

Control structures available in Scratch

Clicking the tan Control button shown at the upper center in Image 4 exposes the blocks shown in Image 11 . As mentioned above, two of the blocks can be used tocreate pure selection structures and one can be used to create a combination of a loop structure and a selection structure. The other blocksserve other purposes.

Selection structures are created by dragging the selection blocks into the rightmost panel in order to apply them to a particularsprite.

Image 11. control structures available in scratch.

Missing image.
Image 11. Control structures available in Scratch.

How do the two if blocks differ?

The if-then-else block in Image 11 is used to select between two specific actions (or two sequences of actions) . The if-then block is used when there is only one action (or one sequence of actions) and you need to decide whether to take that action or not.

That latter case describes the situation in this program. If the basketball is touching a beachball, a specific action is required.If the basketball is not touching a beachball, no specific action is required.

Specifying the condition on which the decision will be based

Note the empty darker depressed area in some of the blocks shown in Image 11 (the rectangles with the pointed ends) . In order to use 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.

Questions & Answers

what does nano mean?
Anassong Reply
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?
Damian Reply
absolutely yes
Daniel
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
Maciej
characteristics of micro business
Abigail
for teaching engĺish at school how nano technology help us
Anassong
Do somebody tell me a best nano engineering book for beginners?
s. Reply
what is fullerene does it is used to make bukky balls
Devang Reply
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
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
Virgil
is Bucky paper clear?
CYNTHIA
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.
Harper
Do you know which machine is used to that process?
s.
how to fabricate graphene ink ?
SUYASH Reply
for screen printed electrodes ?
SUYASH
What is lattice structure?
s. Reply
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
Sanket Reply
what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
China
Cied
types of nano material
abeetha Reply
I start with an easy one. carbon nanotubes woven into a long filament like a string
Porter
many many of nanotubes
Porter
what is the k.e before it land
Yasmin
what is the function of carbon nanotubes?
Cesar
I'm interested in nanotube
Uday
what is nanomaterials​ and their applications of sensors.
Ramkumar Reply
what is nano technology
Sravani Reply
what is system testing?
AMJAD
preparation of nanomaterial
Victor Reply
how to synthesize TiO2 nanoparticles by chemical methods
Zubear
what's the program
Jordan
?
Jordan
what chemical
Jordan
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
Privacy Information Security Software Version 1.1a
Good
Berger describes sociologists as concerned with
Mueller 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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