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Figure 8 . A serious programming problem.
>>>xypdq = 6>>>pzmbw = 5>>>xypdq + pzmbw 11>>>xyppq = 16 # accidental misspelling>>>xypdq + pzmbw # correct spelling 11>>>

Why did this happen ?

The problem arose in the fifth line of text in Figure 8 . In this line, the programmer intended to assign a value of 16 to the existing variable named xypdq. However, because of a spelling error, the programmerinadvertently created a new variable named xyppq and assigned the new value of 16 to the new variable insteadof assigning it to the existing variable.

As a result, the value stored in the original variable named xypdq wasn't changed. When that variable was used later in an expression, the result did not meet theprogrammer's expectations.

The code visualizer

This error is illustrated in the diagram for the code visualizer in Figure 9 .

Figure 9. Visualizer showing result of a spelling error.

missing image

The code in the code window in Figure 9 is similar to the interactive code in Figure 8 .

The diagram on the right in Figure 9 shows a variable named xyppq (not xypdq) that exists solely because of a spelling error when writing the code. That variable should not exist. In addition, that variable points toan object of type int containing a value 16. That object also should not exist. (The computer does exactly what you tell it to do, even if what you tell it to do is wrong.)

Spelling errors can be dangerous

This is one of the greatest dangers of using a programming language that doesn't require the declaration of variables. This type of spelling error iseasy to make (as a result of a simple typing error) , and can be extremely difficult to find and fix.

Defending against spelling errors

The best defense against this kind of error is to make all of your variable names meaningful. Then if you make a typing error (that results in a spelling error) , you might have a better chance of finding it later.

Meaningful variable names

Some meaningful variable names follow. Note the judicious use of upper and lower case to visually break the variable name into separate recognizable words. This is anaming convention that has become very popular, particular among Java programmers. It is commonly referred to as camelCase as in thisCamelHasFourHumps .

  • myUpperLimit
  • yourUpperLimit
  • theOverheadRate
  • theFinalPrice

Remember, case is significant in variable names

The variable named MyUpperLimit is not the same variable as the one named myUpperLimit .


This section contains a variety of miscellaneous information.

Housekeeping material
  • Module name: Itse1359-1030-Variables and Identifiers
  • File: Itse1359-1030.htm
  • Published: 10/14/14
  • Revised: 01/31/16

Financial : Although the Connexions site makes it possible for you to download a PDF file for thismodule at no charge, and also makes it possible for you to purchase a pre-printed version of the PDF file, you should beaware that some of the HTML elements in this module may not translate well into PDF.

I also want you to know that, I receive no financial compensation from the Connexions website even if you purchase the PDF version of the module.

In the past, unknown individuals have copied my modules from cnx.org, converted them to Kindle books, and placed them for sale on Amazon.com showing me as the author. Ineither receive compensation for those sales nor do I know who does receive compensation. If you purchase such a book, please beaware that it is a copy of a module that is freely available on cnx.org and that it was made and published withoutmy prior knowledge.

Affiliation : I am a professor of Computer Information Technology at Austin Community College in Austin, TX.


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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