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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

can someone help me with some logarithmic and exponential equations.
Jeffrey Reply
sure. what is your question?
okay, so you have 6 raised to the power of 2. what is that part of your answer
I don't understand what the A with approx sign and the boxed x mean
it think it's written 20/(X-6)^2 so it's 20 divided by X-6 squared
I'm not sure why it wrote it the other way
I got X =-6
ok. so take the square root of both sides, now you have plus or minus the square root of 20= x-6
oops. ignore that.
so you not have an equal sign anywhere in the original equation?
Commplementary angles
Idrissa Reply
im all ears I need to learn
right! what he said ⤴⤴⤴
what is a good calculator for all algebra; would a Casio fx 260 work with all algebra equations? please name the cheapest, thanks.
Kevin Reply
a perfect square v²+2v+_
Dearan Reply
kkk nice
Abdirahman Reply
algebra 2 Inequalities:If equation 2 = 0 it is an open set?
Kim Reply
or infinite solutions?
The answer is neither. The function, 2 = 0 cannot exist. Hence, the function is undefined.
Embra Reply
if |A| not equal to 0 and order of A is n prove that adj (adj A = |A|
Nancy Reply
rolling four fair dice and getting an even number an all four dice
ramon Reply
Kristine 2*2*2=8
Bridget Reply
Differences Between Laspeyres and Paasche Indices
Emedobi Reply
No. 7x -4y is simplified from 4x + (3y + 3x) -7y
Mary Reply
is it 3×y ?
Joan Reply
J, combine like terms 7x-4y
Bridget Reply
im not good at math so would this help me
Rachael Reply
I'm not good at math so would you help me
what is the problem that i will help you to self with?
how do you translate this in Algebraic Expressions
linda Reply
Need to simplify the expresin. 3/7 (x+y)-1/7 (x-1)=
Crystal Reply
. After 3 months on a diet, Lisa had lost 12% of her original weight. She lost 21 pounds. What was Lisa's original weight?
Chris Reply
what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
types of nano material
abeetha Reply
I start with an easy one. carbon nanotubes woven into a long filament like a string
many many of nanotubes
what is the k.e before it land
what is the function of carbon nanotubes?
what is nanomaterials​ and their applications of sensors.
Ramkumar Reply
what is nano technology
Sravani Reply
what is system testing?
preparation of nanomaterial
Victor Reply
Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
Himanshu Reply
good afternoon madam
what is system testing
what is the application of nanotechnology?
In this morden time nanotechnology used in many field . 1-Electronics-manufacturad IC ,RAM,MRAM,solar panel etc 2-Helth and Medical-Nanomedicine,Drug Dilivery for cancer treatment etc 3- Atomobile -MEMS, Coating on car etc. and may other field for details you can check at Google
anybody can imagine what will be happen after 100 years from now in nano tech world
after 100 year this will be not nanotechnology maybe this technology name will be change . maybe aftet 100 year . we work on electron lable practically about its properties and behaviour by the different instruments
name doesn't matter , whatever it will be change... I'm taking about effect on circumstances of the microscopic world
how hard could it be to apply nanotechnology against viral infections such HIV or Ebola?
silver nanoparticles could handle the job?
not now but maybe in future only AgNP maybe any other nanomaterials
can nanotechnology change the direction of the face of the world
Prasenjit Reply
At high concentrations (>0.01 M), the relation between absorptivity coefficient and absorbance is no longer linear. This is due to the electrostatic interactions between the quantum dots in close proximity. If the concentration of the solution is high, another effect that is seen is the scattering of light from the large number of quantum dots. This assumption only works at low concentrations of the analyte. Presence of stray light.
Ali Reply
the Beer law works very well for dilute solutions but fails for very high concentrations. why?
bamidele Reply
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit 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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