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An introduction to the case control structure and how it is implemented using a switch within the C++ programming language.

Traditional case control structure

Multiway selection using the case structure

One of the drawbacks of two way selection is that we can only consider two choices. But what do you do if you have more than two choices. Consider the following which has four choices:

if age equal to 18 you can voteelse if age equal to 39you're middle aged elseif age equal to 65 consider retirementelse age is un-important

You get an appropriate message depending on the value of age. The last item is referred to as the default. If the age is not equal to 18, 39 or 65 you get the default message. In some situations there is no default action. Consider this flowchart example:

This flowchart is of the case control structure and is used for multiway selection. The decision box holds the variable age. The logic of the case is one of equality where in the value in the variable age is compared to the listed values in order from left to right. Thus, the value stored in age is compared to 18 or is "age equal to 18". If it is true, the logic flows down through the action and drops out at the bottom of the case structure. If the value of the test expression is false, it moves to the next listed value to the right and makes another comparison. It works exactly the same as our nested if then else structure.

C++ code to accomplish multiway selection

Using the same example as above, here is the C++ code to accomplish the case control structure.

C++ source code - case structure with integers

switch (age) {case 18: cout<<"\nYou can vote."; break;case 39: cout<<"\nYou're middle aged."; break;case 65: cout<<"\nConsider retirement."; break;default: cout<<"\nAge is un-important."; }

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The first thing you should note is that the C++ programming language does not formally have a case control structure. It does have a switch control structure but it acts differently than the traditional case control structure. We use a break (which is a branching control structure) with the switch to make it act like the traditional case structure. This is one of the few allowable ways to use the switch with break within the C++ programming language to simulate the traditional case structure. All other uses of the switch or break are to be avoided if you are to stay within the bounds of good structured programming techniques.

The value in the variable age is compared to the first "case" (note: case is one of the C++ reserved words) which is the value 18 (also called the listed value) using an equality comparison or is "age equal to 18". If it is true, the cout is executed which displays “You can vote.” and the next line of code (the break) is done (which jumps us to the end of the control structure). If it is false, it moves on to the next case for comparison.

Most programming languages, including C++, require the listed values for the case control structure be of the integer family of data types. This basically means either an integer or character data type. Consider this example that uses character data type (choice is a character variable):

C++ source code - case structure with characters

switch (choice) {case 'A': cout<<"\nYou are an A student."; break;case 'B': cout<<"\nYou are a B student."; break;case 'C': cout<<"\nYou are a C student."; break;default: cout<<"\nMaybe you should study harder."; }

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Limitations of the case control structure

Most programming languages, including C++, do not allow ranges of values for case like structures. Consider this flowcharting example that used ranges:

Consider also the following pseudocode for the same logic:

Case of age 0 to 17 Display "You can't vote."18 to 64 Display "You’re in your working years." 65 + Display "You should be retired."Endcase

Using the case control structure when using non integer family or ranges of values is allowed when designing a program and documenting that design with pseudocode or flowcharting. However, the implementation in most languages would follow a nested if then else approach with complex Boolean expressions. The logic of the above examples would look like this:

if age>0 and age<= to 17 display You can’t vote.else if age is>= 18 and age<= 64 display You’re in your working years.else display You should be retired.

Good structured programming methods

Most text book authors confirm that good structured programming techniques and habits are more important than concentrating on the technical possibilities and capabilities of the language that you are using to learn programming skills.  Remember, this module is concentrating on programming fundamentals and concepts and it uses the C++ programming language to build our initial programming skills.  It is not a created with the intent to cover the C++ programming language in detail, despite the fact that at times we have to cover C++ language mechanics.

Definitions

case
A control structure that does mulitway selection.
switch
A C++ control structure that can be made to act like a case control structure.

Questions & Answers

where we get a research paper on Nano chemistry....?
Maira Reply
nanopartical of organic/inorganic / physical chemistry , pdf / thesis / review
Ali
what are the products of Nano chemistry?
Maira Reply
There are lots of products of nano chemistry... Like nano coatings.....carbon fiber.. And lots of others..
learn
Even nanotechnology is pretty much all about chemistry... Its the chemistry on quantum or atomic level
learn
Google
da
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Bhagvanji
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Giriraj
Preparation and Applications of Nanomaterial for Drug Delivery
Hafiz Reply
revolt
da
Application of nanotechnology in medicine
what is variations in raman spectra for nanomaterials
Jyoti Reply
ya I also want to know the raman spectra
Bhagvanji
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Crow Reply
what about nanotechnology for water purification
RAW Reply
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
Damian
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Professor
I think
Professor
Nasa has use it in the 60's, copper as water purification in the moon travel.
Alexandre
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Alexandre
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
Rafiq
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
Damian
How we are making nano material?
LITNING Reply
what is a peer
LITNING Reply
What is meant by 'nano scale'?
LITNING Reply
What is STMs full form?
LITNING
scanning tunneling microscope
Sahil
how nano science is used for hydrophobicity
Santosh
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
Rafiq
what is differents between GO and RGO?
Mahi
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
Rafiq
if virus is killing to make ARTIFICIAL DNA OF GRAPHENE FOR KILLED THE VIRUS .THIS IS OUR ASSUMPTION
Anam
analytical skills graphene is prepared to kill any type viruses .
Anam
Any one who tell me about Preparation and application of Nanomaterial for drug Delivery
Hafiz
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Damian
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
Renato
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
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
Adin
why?
Adin
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
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Source:  OpenStax, Programming fundamentals - a modular structured approach using c++. OpenStax CNX. Jan 10, 2013 Download for free at http://cnx.org/content/col10621/1.22
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