A Complete Guide to Programming in C++ part 34 doc

Article const Article& ; Copy constructor of class Article The copy constructor creates a copy of an existing object.The parameter is thus a read-only reference to the object that needs

䊐 Definition

An enumeration is a user-definable, integral type An enumeration is defined using the enumkeyword A range of values and a name for these values are also defined at the same time

Example: enum Shape{ Line, Rectangle, Ellipse};

This statement defines the enumerated type Shape The names quoted in the list iden-tify integral constants Their values can be deduced from the list order The first constant has a value of 0, and each subsequent constant has a value that is one higher than its predecessor

In the previous example, Linethus represents a value of 0,Rectanglea value of 1, andEllipsea value of 2 A Shapetype variable can only assume one of these values

Example: Shape shape = Rectangle; // Variable shape

//

switch(shape) // To evaluate shape

{

case Line: // etc

However, you can also define the values of the constants explicitly

Example: enum Bound { Lower = -100, Upper = 100};

You can leave out the type name, if you only need to define the constants

Example: enum { OFF, OUT=0, ON, IN=1 };

This statement defines the constants OFFandOUT, setting their value to 0, and the con-stantsONandINwith a value of 1 The values for OFFandONare implicit

䊐 Class-Specific Constants

Enumeration can be used to define integral symbolic constants in a simple way In con-trast to #definedirectives, which merely replace text strings, enumconstants are part

of a declaration and thus have a valid range This allows you to define constants that are visible within a namespace or class only

The example on the opposite page shows the enumerated type State, which was defined within the Lightsclass This means that the type and enumconstant are only available for direct use within the class The enumeration itself is declared as public, however, and access from outside the class is therefore possible

Example: if(Lights.getState() == Lights::red)

//

Article( const Article& );

Copy constructor of class Article

The copy constructor creates a copy of an existing object.The parameter is thus

a read-only reference to the object that needs to be copied.The copy constructor in the Articleclass is thus declared as follows:

Declaration of copy constructor:

The default copy constructor simply transfers the data members to the new object.

The Member Class

int string const Date

Member Number Name

Birthday

//Possibly more information, such as an address, telephone number, .

Constructor with one parameter for each data member Access methods for each data member The birthday is read-only.

A method for formatted screen output of all data members

Private Data Members

Public Methods

Type

Exercise 1

In the first exercise of the last chapter you defined a simple class called

Article.This involved using a global counter to log object creation and

destruction Improve and extend the Articleclass as follows:

■ Use a static data member instead of a global variable to count the current number of objects.

■ Declare a static access method called getCount()for the Articleclass The method returns the current number of objects.

■ Define a copy constructor that also increments the object counter by 1 and issues a message.This ensures that the counter will always be accu-rate.

Tip: Use member initializers.

■ Test the new version of the class.To do so, call the function test()by passing an article type object to the function.

Exercise 2

A sports club needs a program to manage its members.Your task is to define and test a class called Memberfor this purpose.

■ Define the Memberclass using the data members shown opposite Use theDateclass defined in the last chapter for your definition Since a member’s birthday will not change, the data member for birthdays must

be defined as a const.

Overload the constructor to allow for entering a date as an object as well as three values for day, month, and year.

■ Implement the necessary methods.

■ Test the new Memberclass by creating at least two objects with the data

of your choice and calling the methods you defined.

■ Add a static member called ptrBossto the class.This pointer indicates the member who has been appointed as chairperson If no chairperson has been appointed, the pointer should point to NULL.

■ Additionally, define the static access methods getBoss()andsetBoss() Use a pointer to set and return the object in question.

■ Test the enhanced Memberclass by reading the number of an existing member, making the member the new chairperson and displaying the chairperson using getBoss().

Simulation of two traffic lights!

Terminate this program with <Ctrl>+<C>!

1 Light 2 Light -RED AMBER

GREEN AMBER AMBER RED GREEN

AMBER RED AMBER

GREEN //

Hints for implementing the function wait()

1 The function time() is declared in the header file ctime The call time(NULL) determines the number of seconds of type time_t since 1.1.1970, 0:0 hours.The type time_tis defined as long.

2 Instead of calling the function time() in a loop, you can use the function Sleep() for Windows or the function sleep() for Unix These system calls are not standardized, yet they are much more effective because they send a process to sleep instead of using a waiting loop.

Exercise 3

Create a program to simulate the signal positions for two sets of traffic lights at

a junction Use the class Lightsas defined in this chapter for your program.

■ Each set of lights is switched through the phases red, amber, green, amber, red, and so on.You must ensure that one set of lights can be only in the amber or green state when the other set of lights is red.

■ The lights operate in an infinite loop that can be terminated by interrupt-ing the program.You can use the key combination <Ctrl>+<C> for DOS and Windows and the Interrupt key, i.e., normally the <Del> key, for UNIX.

■ The status of the lights is constant for a certain number of seconds For example, the green phase can take 20 seconds and the amber phase 1 second.These values can be different for each set of lights Define an auxiliary function

inline void wait( int sec)

The function returns after the stipulated number of seconds.To do so, you can call the standard function time()in a loop Don’t forget to read the notes on the opposite page.

Exercise 1

// -// article.h

// Defines a simple class - Article

//

-#ifndef _ARTICLE_H_

#define _ARTICLE_H_

#include <string>

using namespace std;

class Article {

private:

long nr; // Article number string name; // Article name double sp; // Sales price // Static data member:

static int countObj; // Number of objects public:

Article( long nr=0, const string& name="noname",

double sp=0.0);

// Copy constructor:

Article( const Article& anArticle);

~Article();

void print();

// Access methods:

const string& getName() const { return name; } long getNr() const { return nr; } double getSP() const { return sp; } static int getCount() { return countObj; } bool setName( const string& s)

{ if( s.size() < 1) // No empty Name return false;

name = s;

return true;

} void setNr( long n) { nr = n; } void setSP(double v)

{ // No negative price

sp = v > 0.0 ? v : 0.0;

} };

#endif // _ARTICLE_

//

-// article.cpp

// Methods of Article, which are not defined as inline

// Constructor and destructor output when called

//

-#include "article.h" // Definition of the class

#include <iostream>

#include <iomanip>

using namespace std;

// Defining the static data member:

int Article::countObj = 0; // Number of objects

// Defining the constructor and destructor:

Article::Article( long nr, const string& name, double sp)

{

setNr(nr); setName(name); setSP(sp);

++countObj;

cout << "An article \"" << name

<< "\" is created.\n"

<< "This is the " << countObj << " article!"

<< endl;

}

// Defining the copy constructor:

Article::Article( const Article& art)

:nr(art.nr), name(art.name), sp(art.sp)

{

++countObj;

cout << "A copy of the article \"" << name

<< "\" is generated.\n"

<< "This is the " << countObj << " article!"

<< endl;

}

Article::~Article()

{

cout << "The article \"" << name

<< "\" is destroyed.\n"

<< "There are still " << countObj << " articles!"

<< endl;

}

// The method print() outputs an article

void Article::print()

{

// As before! Compare to the solutions of chapter 14

}

// article_t.cpp

// Tests the class Article including a copy constructor //

-#include "article.h" // Definition of the class

#include <iostream>

#include <string>

using namespace std;

void test( Article a); // Prototype Article article1( 1111,"tent", 159.9); // Global int main()

{ cout << "\nThe first statement in main().\n" << endl; Article article2( 2222,"jogging shoes", 199.99);

cout << "\nThe first call of test()." << endl;

test(article1); // Passing by Value cout << "\nThe second call of test()." << endl;

test(article2); // Passing by Value cout << "\nThe last statement in main().\n"

<< "\nThere are still " << Article::getCount()

<< " objects\n" << endl;

return 0;

}

void test( Article a) // Calls the copy constructor {

cout << "\nThe given object:" << endl;

a.print();

static Article bike( 3333, "bicycle", 999.0);

cout << "\nThe static object in function test():"

<< endl;

bike.print();

cout << "\nThe last statement in function test()"

<< endl;

}

Exercise 2

TheDateclass from the last chapter ( see files Date.handDate.cpp) can be left unchanged But it makes sense to define the function isLeapYear()as a static member function of class Daterather than globally.

The other files:

//

-// member.h

// Defines the Member class containing a constant

// and a static member

//

-#ifndef _MEMBER_H_

#define _MEMBER_H_

#include "Date.h"

#include <string>

using namespace std;

class Member

{

private:

int nr; // Member number

string name; // Name

const Date birth; // Birthday

// more data

static Member *ptrBoss; // Pointer to boss,

// NULL = no boss

public:

Member( long m_nr, const string& m_name,

const Date& m_birth) : nr(m_nr), birth(m_birth)

{

if( !setName(m_name)) name = "Unknown";

}

Member( long m_nr, const string& m_name,

int day, int month, int year) : nr(m_nr), birth(day,month,year)

{

if( !setName(m_name)) name = "Unknown";

}

int getNr() const { return nr; }

const string& getName() const { return name; }

const Date& getBirthday() const { return birth; }

void setNr( int n) { nr = n; }

{ if( s.size() < 1) // No empty name return false;

name = s;

return true;

} void display() const;

// static methods:

static Member* getBoss() {

return ptrBoss;

} static void setBoss( Member* ptrMem) {

ptrBoss = ptrMem;

} };

#endif // _MEMBER_H_

// -// member.cpp

// Members of class Member not defined inline

//

-#include "member.h" // Class definition

#include <iostream>

using namespace std;

// Pointer to the boss:

Member* Member::ptrBoss = NULL;

void Member::display() const {

string line( 50, '-');

cout << line

<< "\n Member number: " << nr

<< "\n Member: " << name

<< "\n Birthday " << birth.asString()

<< '\n' << line << endl;

}