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Most computer programs that solve real-world problems are much larger than the programs in the first few chapters. Experience has shown that the best way to develop and maintain a large program is to construct it from smaller pieces or program units each, of which is more manageable than the original program. Generally, user-defined program units are called subprograms. This technique is called divide-and-conquer. This chapter deals with the method of declaration of the user-defined function and its use in C++. Besides, this chapter also covers pointer data type which is one of the strength of the C++ language.

Function and parameter declarations

In C++ all subprograms are referred to as functions . A function allows you to treat a related group of C++ statements as a single unit. The programmer can write functions to define specific tasks that could be used at many points in a program.

Functions allow the programmer to modulize a program. All variables declared in function definitions are local variables – they are known only in the function in which they are defined. Most functions have a list of parameters that provide the means for communicating information between functions.

There are several motivations for dividing a program into functions. The divide-and-conquer approach makes program development more manageable. Another motivation is software reusability – using existing functions as building blocks to create new programs. Software reusability is a major factor in object-oriented programming. With good function naming and definition, programs can be created from standardized functions that accomplish specific tasks. A third motivation is to avoid repeating code in a program. Packing code as a function allows the code to be executed from several location in a program simply by calling the function.

Defining a function

The lines that compose a function within a C++ program are called a function definition. The syntax for defining a function is

data_type name_of_function (parameters){



A function definition consists of four parts:

- A reserved word indicating the return data type of the function’s return value.

- The function name

- Any parameters required by the function, contained within parentheses.

- The function’s statements enclosed in curly braces { }.

Example: The following function determines the largest integer among three parameters passed to it.

int maximum( int x, int y, int z )


int max = x;

if ( y>max )

max = y;

if ( z>max )

max = z;

return max;


You designate a data type for function since it is common to return a value from a function after it executes.

General format of a function is described below.

General format of a function

Variable names that will be used in the function header line are called formal parameters.

How to call functions

To execute a function, you must invoke, or call, it from the main () function.

The values or variables that you place within the parentheses of a function call statement are called arguments or actual parameters.

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
Difference between extinct and extici spicies
Amanpreet Reply
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Source:  OpenStax, Programming fundamentals in c++. OpenStax CNX. Jul 29, 2009 Download for free at http://cnx.org/content/col10788/1.1
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