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Preventing multiple inclusion

Large class-based programs are sometimes composed of multiple interface and implementation files. With large program, you need to ensure that you do not include multiple instances of the same header file when you compile the program, since multiple inclusion will make your program unnecessary large.

C++ generates an error if you attempt to compile a program that includes multiple instances of the same header file. To prevent this kind of error, most C++ programmers use the #define preprocessor directive with the #if and #endif preprocessor directives in header files.

The #if and #endif preprocessor directives determine which portions of a file to compile depending on the result of a conditional expression.

The syntax for the #if and #endif preprocessor directives:

#if conditional expression

statements to compile;

#endif

Example:

#if !defined(TIME1_H)

#define TIME1_H

class Time {

public:

Time();

void setTime( int, int, int );

void printMilitary();

void printStandard();

private:

int hour;

int minute;

int second;

};

#endif

Note: Common practice when defining a header file’s constant is to use the header file’s name in uppercase letters appended with H. For example, the constant for the time1.h header file is usually defined as TIME1_H.

Member functions

In this section, we learn how to write member functions for a class.

Inline functions

Although member functions are usually defined in an implementation file, they can also be defined in an interface file. Functions defined inside the class body in an interface file are called inline functions .

Example:

class Stocks {

public:

double getTotalValue(int iShares, double dCurPrice){

double dCurrentValue;

iNumShares = iShares;

dCurrentPricePerShare = dCurPrice;

dCurrentValue = iNumShares*dCurrentPricePerShare;

return dCurrentValue;

}

private:

int iNumShares;

double dPurchasePricePerShare;

double dCurrentPricePerShare;

};

Diagram of class stock

Member functions in implementation file

Member function definitions are always placed in the implementation file.

In the example below, for the class Stocks, the definition of the member function getTotalValue is placed in the source-code file stocks.cpp in which the main program is also included.

Example

//stocks.h ---------------- interface section

#if !defined(STOCKS_H)

#define STOCKS_H

class Stocks{

public:

double getTotalValue(int iShares, double dCurPrice);

private:

int iNumShares;

double dPurchasePricePerShare;

double dCurrentPricePerShare;

};

#endif

// stocks.cpp ----------------- implementation section

#include “stocks.h”

#include<iostream.h>

double Stocks::getTotalValue(int iShares, double dCurPrice){

double dCurrentValue;

iNumShares = iShares;

dCurrentPricePerShare = dCurPrice;

dCurrentValue = iNumShares*dCurrentPricePerShare;

return dCurrentValue;

}

int main(){

Stocks stockPick;

cout<<stockPick.getTotalValue(200, 64.25)<<endl;

return 0;

}

Output of the above program:

12850

Note: The format of member functions included in the implementation section is as follows:

return-type Class-name::functionName(parameter-list)

Questions & Answers

can someone help me with some logarithmic and exponential equations.
Jeffrey Reply
sure. what is your question?
ninjadapaul
20/(×-6^2)
Salomon
okay, so you have 6 raised to the power of 2. what is that part of your answer
ninjadapaul
I don't understand what the A with approx sign and the boxed x mean
ninjadapaul
it think it's written 20/(X-6)^2 so it's 20 divided by X-6 squared
Salomon
I'm not sure why it wrote it the other way
Salomon
I got X =-6
Salomon
ok. so take the square root of both sides, now you have plus or minus the square root of 20= x-6
ninjadapaul
oops. ignore that.
ninjadapaul
so you not have an equal sign anywhere in the original equation?
ninjadapaul
Commplementary angles
Idrissa Reply
hello
Sherica
im all ears I need to learn
Sherica
right! what he said ⤴⤴⤴
Tamia
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?
Kim
The answer is neither. The function, 2 = 0 cannot exist. Hence, the function is undefined.
Al
y=10×
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
yes
Asali
I'm not good at math so would you help me
Samantha
what is the problem that i will help you to self with?
Asali
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
China
Cied
types of nano material
abeetha Reply
I start with an easy one. carbon nanotubes woven into a long filament like a string
Porter
many many of nanotubes
Porter
what is the k.e before it land
Yasmin
what is the function of carbon nanotubes?
Cesar
what is nanomaterials​ and their applications of sensors.
Ramkumar Reply
what is nano technology
Sravani Reply
what is system testing?
AMJAD
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
AMJAD
what is system testing
AMJAD
what is the application of nanotechnology?
Stotaw
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
Azam
anybody can imagine what will be happen after 100 years from now in nano tech world
Prasenjit
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
Azam
name doesn't matter , whatever it will be change... I'm taking about effect on circumstances of the microscopic world
Prasenjit
how hard could it be to apply nanotechnology against viral infections such HIV or Ebola?
Damian
silver nanoparticles could handle the job?
Damian
not now but maybe in future only AgNP maybe any other nanomaterials
Azam
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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