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Eventually all of the actions will be completed and the condition will be tested again.

Need to avoid infinite loops

Generally speaking, unless something is done in one of the actions to cause the test to eventually return false, control will never exit the loop.

In this case, the program will be caught in what is commonly referred to as an infinite loop.

Other possible structures

In some programming languages, there are structures other than sequence, selection, and loop that structured-programming experts are willing toaccept for convenience including:

  • The switch-case structure.
  • The do-until structure.
  • The for loop
  • The for-each loop

While sometimes more convenient than the three main structures, these structures are not required for the solution of programming logic problems.


In this module, I will present and explain the simplest example of a selection structure that I was able to write in Scratch without using variablesand without using relational or logical operators. (I will explain operators, including relational and logical operators in future modules.)

Screen output for the program named IfSimple01

The program places a basketball and two beach balls on the Stage as shown in Image 4 .

Image 4. user interface for the program named ifsimple01.

Missing image.
Image 4. User interface for the program named IfSimple01.

Click the green flag or the basketball

When the user clicks the green flag in the upper right corner, the three balls are placed in a horizontal line with the basketball in the center.

Scratch code, which can be paraphrased as shown in Image 5 , is executed each time the user clicks the basketball with the mouse.

Image 5. a paraphrased version of the scratch code.

when Basketball is clicked{ move basketball forward by 90 stepsif(Basketball is touching RightBeachball){ turn Basketball by 180 degrees}//end ifif(Basketball is touching LeftBeachball){ turn Basketball by 180 degrees}//end if }
Image 5. A paraphrased version of the Scratch code.

In other words, if you repetitively click the basketball with the mouse, it will move back and forth from left to right bouncing off of the two beach balls.The basketball will keep bouncing back and forth between the two beach balls for as long as you continue clicking on the basketball.

Discussion and sample code

Let's walk through the steps required to develop this program. I will deal first with the code that defines the behavior of the program when the userclicks the green flag in the upper right corner of Image 4 .

The Cartesian coordinate system The position of sprites on the Stage in the Scratch user interface is based on a two-dimensional Cartesian coordinate system with the origin at the center of the Stage.

Three sprites

Note in the lower right corner of Image 4 that this program contains two beach balls and one basketball in addition to the Stage.

You add sprites to your program by clicking on the button with the icon of the file folder in the grayarea immediately below the white Stage area in Image 4 .

When you click on one of the sprites that you have added to the program, that sprite appears at the top of the center pane. Having done that, you canthen drag programming blocks into the center pane that define the behavior of that sprite.

Questions & Answers

what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
scanning tunneling microscope
how nano science is used for hydrophobicity
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
what is differents between GO and RGO?
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
The nanotechnology is as new science, to scale nanometric
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
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
How can I make nanorobot?
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
how can I make nanorobot?
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.
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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