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Example: Function maximum is invoked or called in main() with the call

maximum(a, b, c)

Function prototypes

One of the most important features of C++ is the function prototype. A function prototype declares to the compiler that you intend to use a function later in the program. It informs the compiler the name of the function, the type of data returned by the function, the number of parameters the function expects to receive, the types of the parameters and the order in which these parameters are expected. The compiler uses function prototypes to validate function calls.

If you try to call a function at any point in the program prior to its function prototype or function definition, you will receive an error when you compile the project.


// Finding the maximum of three integers


int maximum(int, int, int); // function prototype

int main()


int a, b, c;

cout<<"Enter three integers: ";


// a, b and c below are arguments to the maximum function call

cout<<"Maximum is: "<<maximum (a, b, c)<<endl;

return 0;


// Function maximum definition

// x, y and z are parameters to the maximum function definition

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


int max = x;

if ( y>max )

max = y;

if ( z>max )

max = z;

return max;


The output of the above program:

Enter three integers: 22 85 17

Maximum is: 85

Passing by value

If a variable is one of the actual parameters in a function call, the called function receives a copy of the values stored in the variable. After the values are passed to the called function, control is transferred to the called function.

Example: The expression maximum( a, b, c) calls the function maximum() and causes the values currently residing in the variables a, b and c to be passed to maximum().

The method of passing values to a called function is called pass by value.

Functions with empty parameter lists

Functions may have empty parameter list. The function prototype for such a function requires either the keyword void or nothing at all between the parentheses following the function name.


int display();

int display(void);

Returning values

To actually return a value, the function must use a return statement, which has the form:

return expression;



Remember that values passes back and forth between functions must be of the same data type.

When the return statement is encountered, the expression is evaluated first. The value of the expression is then automatically converted to the data type declared in the function header before being sent back to the calling function. After the value is returned, program control reverts to the calling function.

Inline functions

For small functions, you can use the inline keyword to request that the compiler replace calls to a function with the function definition wherever the function is called in a program.


// Using an inline function to calculate

// the volume of a cube.


inline double cube(double s) { return s * s * s; }

int main()


cout<<"Enter the side length of your cube: ";

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
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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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