# 1.7 Scr0370: the repeat loop in scratch 2.0  (Page 2/7)

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## General background information

In an earlier module (see Resources ) , I told you that any programming logic problem could be solved using anappropriate combination of only three programming structures, none of which are complicated. The three structures are known generally as:

• The sequence structure.
• The selection or decision structure.
• The loop, repetition, or iteration structure.

I explained the sequence and selection structures in earlier modules. I will concentrate on the loop structure in this and the next module.

## Definite versus indefinite loops

Loop structures in programming fall into two broad categories:

• Definite loops
• Indefinite loops

There are numerous sub-categories within these broad categories. I will illustrate the difference between a definite loop and an indefinite loop with two real-world examples.

## A definite loop example

Assume that you are confronted with a full box of cookies. Assume also that you have more self-control than most of us, and that you decide you can eatthree cookies, but no more than three, in order to keep your waistline under control. You might eat the three cookies using an algorithm something like thatshown in Image A .

## Explanation of the definite loop

Being the self-controlled individual that you are, you would set your cookie limit to 3 and you would set count to 1. You would then test count to see if it is within the range from 1 to 3 inclusive. If so, you would take acookie from the box and eat it. Then you would increase the value of count by 1 and go back to the top of the loop.

Back at the top of the loop, you would once again test the value of count to determine if it is still within the range from 1 to 3 inclusive. If so, youwould repeat the process, getting and eating another cookie, increasing the value of count by 1, and going back to the top of the loop.

When you find that the value of count has advanced to 4, you would recognize that this is outside the range of 1 to 3 inclusive. As a result, youwould terminate the loop and stop eating cookies. Well done!

## An indefinite loop example

Assume once again that you are confronted with the same full box of cookies. However, like many of us, you aren't blessed with a lot of self-control. In thatcase, you might eat cookies using the algorithm shown in Image B .

## Explanation of the indefinite loop

Unfortunately, for many of us, as soon as we see the full box of cookies, our stillHungry variable gets set to true.

We begin the process by performing a test to determine if stillHungry is true and the box of cookies is not empty. If that test returns true, we take a cookie from the box and eat it. Then we perform another test. If weare no longer hungry at that point, we set our stillHungry variable to false and go back to test at the top of the loop. Otherwise, we allow our stillHungry variable to remain true.

Back at the top of the loop, we test again to determine if stillHungry is true, and the box of cookies is not empty. If the test returns true, we gothrough the process again, eating another cookie, etc.

anyone know any internet site where one can find nanotechnology papers?
research.net
kanaga
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
what's the easiest and fastest way to the synthesize AgNP?
China
Cied
types of nano material
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.
how did you get the value of 2000N.What calculations are needed to arrive at it
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