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  • You may not remove a slip of paper from a compartment without replacing it by another slip of paper on which you have written a value.
  • You may not put a slip of paper in a compartment without removing the one already there.

Checkout counter example

In understanding how you might behave as a human computer program, consider yourself to have a job working at the checkout counter of a small grocery store in the 1930s.

You have two tools to work with:

  • A mechanical adding machine
  • The rack of compartments described above


Each morning, the owner of the grocery store tells you to insert a name in the slot above each compartment and to place a little slip of paper with a number written on it inside each compartment. (In programming jargon, we would refer to this as initialization.)

Each of the names on the compartments represents a type of grocery such as

  • Beans
  • Apples
  • Pears

No two compartments can have the same name.

No compartment is allowed to have more than one slip of paper inside it.

The price of a can of beans

When you place a new slip of paper in a compartment, you must be careful to remove and destroy the one that was already there.

Each slip of paper that you insert into a compartment contains the price for the type of grocery identified by the label on the compartment.

For example, the slip of paper in the compartment labeled Beans may contain the value 15, meaning that each can of beans costs 15 cents.

The checkout procedure

As each customer comes to your checkout counter during the remainder of the day, you execute the following procedure:

  • Examine each grocery item to determine its type.
  • Read the price stored in the compartment corresponding to that type of grocery.
  • Add that price to that customer's bill using your mechanical adding machine.

In programming jargon, we would say that as you process each grocery item for the same customer, you are looping . We would also say that you are executing a procedure or an algorithm .

When you have processed all of the grocery items for a particular customer, you would

  • Press the TOTAL key on the adding machine,
  • Turn the crank, and
  • Present the customer with the bill.

A schematic representation of the procedure

We might represent the procedure in schematic form as shown in Figure 1 .

Figure 1 . A checkout counter algorithm.
For each customer, do the following: For each item, do the following:a. Identify the type of grocery item b. Get the price from the compartmentc. Add the price to accumulated total End loop on grocery itemsPresent customer with a bill End loop on a specific customer

Common programming activities

This procedure illustrates the three activities commonly believed to be the fundamental activities of any computer program:

  • sequence
  • selection
  • loop


A sequence of operations is illustrated by the three items labeled a, b, and c in Figure 1 because they are executed in sequential order.


The process of identifying the type of grocery item is often referred to as selection . A selection operation is the process of selecting among two or more choices.

Questions & Answers

How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
scanning tunneling microscope
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.
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
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