1 c++ structures starting to think about objects

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C++ StructuresC++ Structures

Starting to think about objectsStarting to think about objects......

StructureStructure

A Structure is a container, it can hold a A Structure is a container, it can hold a bunch of bunch of thingsthings..– These things can be of any type.These things can be of any type.

Structures are used to organize related data Structures are used to organize related data (variables) into a nice neat package.(variables) into a nice neat package.

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Example - Student RecordExample - Student Record

Student Record:Student Record:– Name Name a stringa string– HW GradesHW Grades an array of 3 doublesan array of 3 doubles– Test GradesTest Grades an array of 2 doublesan array of 2 doubles– Final AverageFinal Average a doublea double

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Structure MembersStructure Members

Each Each thingthing in a structure is called in a structure is called member.member.

Each Each membermember has a name, a type and a value.has a name, a type and a value.

Names follow the rules for variable names.Names follow the rules for variable names.

Types can be any defined typeTypes can be any defined type..

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Example Structure DefinitionExample Structure Definition

struct StudentRecord {struct StudentRecord {

char *name;char *name; // student name// student name

double hw[3];double hw[3]; // homework grades// homework grades

double test[2];double test[2]; // test grades// test grades

double ave;double ave; // final average// final average

};};

Using a structUsing a struct

By defining a structure you create a new By defining a structure you create a new data type.data type.

Once a struct is defined, you can create Once a struct is defined, you can create variables of the new type.variables of the new type.

StudentRecord stu;StudentRecord stu;

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Accessing MembersAccessing Members You can treat the members of a struct You can treat the members of a struct

just like variables.just like variables. You need to use the You need to use the member access member access

operator operator '.' (pronounced "dot"): '.' (pronounced "dot"):

cout << stu.name << endl;cout << stu.name << endl;

stu.hw[2] = 82.3;stu.hw[2] = 82.3;

stu.ave = total/100; stu.ave = total/100;

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Structure AssignmentStructure Assignment

You can use structures just like variables:You can use structures just like variables:

StudentRecord s1,s2;StudentRecord s1,s2;

s1.name = "Joe Student";s1.name = "Joe Student";

……

s2 = s1;s2 = s1; Copies the entire structure

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Be CarefulBe CarefulIf a member is a pointer, If a member is a pointer, copyingcopying means means

copying the pointer (not what is pointed copying the pointer (not what is pointed to)to)..

name

ave

test

hw

"Joe Student"

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Probably not what you wantProbably not what you want

StudentRecord s1,s2;StudentRecord s1,s2;

s1.name = "Joe Student";s1.name = "Joe Student";

……

s2 = s1;s2 = s1;

s2.name = "Jane Doe";s2.name = "Jane Doe";

// now s1.name and s2.name are both// now s1.name and s2.name are both

// "Jane Doe"// "Jane Doe"

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Pointers to StructuresPointers to Structures

Pointers to structures are used often.Pointers to structures are used often. There is another There is another member access member access

operatoroperator used with pointers: used with pointers: ->->

StudentRecord *sptr;StudentRecord *sptr;

……

cout << "Name is" << cout << "Name is" << sptr->namesptr->name; ;

cout << "Ave is " << cout << "Ave is " << sptr->avesptr->ave;;

it looks like a "pointer

!"

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Sample Function (won't work!)Sample Function (won't work!)

void update_average( StudentRecord stu) {void update_average( StudentRecord stu) {

double tot=0;double tot=0;

for (int i=0;i<3;i++)for (int i=0;i<3;i++)

tot += stu.hw[i];tot += stu.hw[i];


tot += stu.test[i];tot += stu.test[i];

stu.ave = tot/5;stu.ave = tot/5;

}}

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This one worksThis one works

void update_average( StudentRecord *stu)void update_average( StudentRecord *stu){ {

double tot=0double tot=0;;


tot += stu->hw[i]tot += stu->hw[i];;


tot += stu->test[i]tot += stu->test[i];;

stu->ave = tot/5stu->ave = tot/5;;

}}

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Or use a reference parameterOr use a reference parameter

void update_average( StudentRecord &stu) {void update_average( StudentRecord &stu) {

double tot=0;double tot=0;


tot += stu.hw[i];tot += stu.hw[i];


tot += stu.test[i];tot += stu.test[i];

stu.ave = tot/5;stu.ave = tot/5;

}}

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Other stuff you can do with a Other stuff you can do with a structstruct

You can also associate special functions You can also associate special functions with a structure (called with a structure (called member functionsmember functions).).

A C++ A C++ classclass is very similar to a structure, we is very similar to a structure, we will focus on classes.will focus on classes.– Classes can have (data) membersClasses can have (data) members– Classes can have member functions.Classes can have member functions.– Classes can also Classes can also hidehide some of the members some of the members

(functions and data).(functions and data).

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Quick ExampleQuick Examplestruct StudentRecord {struct StudentRecord {

char *name; // student namechar *name; // student name

double hw[3]; // homework double hw[3]; // homework gradesgrades

double test[2]; // test gradesdouble test[2]; // test grades

double ave; // final averagedouble ave; // final average

void print_ave() {void print_ave() {

cout << "Name: " << name << endl;cout << "Name: " << name << endl;

cout << "Average: " << ave << endl;cout << "Average: " << ave << endl;

}}

};};

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Using the member functionUsing the member function

doubleStudentRecord studoubleStudentRecord stu;;

// … // …set values in the structureset values in the structure

stu.print_avestu.print_ave ;)( ;)(

C++ Classes C++ Classes &&

Object Oriented ProgrammingObject Oriented Programming

Exerted fromExerted from: : elearning.najah.edu/OldData/pdfs/elearning.najah.edu/OldData/pdfs/C++C++%20%20ClassesClasses%20Tutorials.%20Tutorials.pptppt


Programmer Programmer thinksthinks about and defines the about and defines the attributes and behavior of objects.attributes and behavior of objects.

Often the objects are modeled after real-Often the objects are modeled after real-world entities.world entities.

Very different approach than Very different approach than function-basedfunction-based programming (like C).programming (like C).


Object-oriented programming (OOP) Object-oriented programming (OOP) – Encapsulates data (attributes) and functions Encapsulates data (attributes) and functions

(behavior) into packages called classes.(behavior) into packages called classes. So, Classes are user-defined (programmer-So, Classes are user-defined (programmer-

defined) types.defined) types.– Data (data members) Data (data members) – Functions (member functions or methods)Functions (member functions or methods)

In other words, they are structures + In other words, they are structures + functionsfunctions

Classes in C++Classes in C++

A class definition begins with the keyword A class definition begins with the keyword classclass..

The body of the class is contained within a The body of the class is contained within a set of braces, set of braces, { } ;{ } ; (notice the semi-colon). (notice the semi-colon).

class class_name}.….….…;{

Class body (data member + methodsmethods)

Any valid identifier

Classes in CClasses in C++++

Within the body, the keywords Within the body, the keywords private:private: and and public:public: specify the access level of the specify the access level of the members of the class.members of the class.– the default is the default is privateprivate..

Usually, the data members of a class are Usually, the data members of a class are declared in the declared in the private:private: section of the class section of the class and the member functions are in and the member functions are in public:public: section.section.


class class_name}

private:………

public:………

;{

Public members or methods

private members or methods


Member access specifiersMember access specifiers

– publicpublic: : can be accessed outside the class directly.can be accessed outside the class directly.

– The public stuff is The public stuff is the interfacethe interface..

– privateprivate:: Accessible only to member functions of classAccessible only to member functions of class Private members and methods are for internalPrivate members and methods are for internal use use

only.only.

Class ExampleClass Example

This class example shows how we can This class example shows how we can encapsulate (gather) a circle information into encapsulate (gather) a circle information into one package (unit or class) one package (unit or class)

class Circle{ private:

double radius; public:

void setRadius(double r);double getDiameter();

double getArea();double getCircumference();

};

No need for others classes to access and retrieve its value directly. The class methods are responsible for that only.

They are accessible from outsidethe class, and they can access themember (radius)

Creating an object of a ClassCreating an object of a Class

Declaring a variable of a class type creates an Declaring a variable of a class type creates an objectobject. You can have many variables of the same . You can have many variables of the same type (class).type (class).– InstantiationInstantiation

Once an object of a certain class is instantiated, a Once an object of a certain class is instantiated, a new memory location is created for it to store its new memory location is created for it to store its data members and codedata members and code

You can instantiate many objects from a class You can instantiate many objects from a class type.type.– Ex) Circle c; Circle *c; Ex) Circle c; Circle *c;

Special Member FunctionsSpecial Member Functions

ConstructorConstructor::– Public function memberPublic function member– called when a new object is created called when a new object is created

(instantiated).(instantiated).– Initialize data members.Initialize data members.– Same name as classSame name as class– No return typeNo return type– Several constructorsSeveral constructors

Function overloadingFunction overloading

Special Member FunctionsSpecial Member Functions



Circle();Circle(int r); void setRadius(double r);double getDiameter();double getArea();double getCircumference();

};

Constructor with no argument

Constructor with one argument

Implementing class methodsImplementing class methods

Class implementation: writing the code of class Class implementation: writing the code of class methods.methods.

There are two ways:There are two ways:1.1. Member functions defined outside classMember functions defined outside class

Using Binary scope resolution operator (Using Binary scope resolution operator (::::)) ““Ties” member name to class nameTies” member name to class name Uniquely identify functions of particular classUniquely identify functions of particular class Different classes can have member functions with same Different classes can have member functions with same

namename– Format for defining member functionsFormat for defining member functions

ReturnTypeReturnType ClassNameClassName::::MemberFunctionNameMemberFunctionName( ){( ){……

}}

Implementing class methodsImplementing class methods

2.2. Member functions defined inside classMember functions defined inside class– Do not need scope resolution operator, class Do not need scope resolution operator, class

name;name;class Circle{ private:


Circle() { radius = 0.0;}Circle(int r);void setRadius(double r){radius = r;}double getDiameter(){ return radius *2;}double getArea();double getCircumference();

};

Defined inside class




};Circle::Circle(int r){ radius = r;}double Circle::getArea(){ return radius * radius * (22.0/7);}double Circle:: getCircumference(){ return 2 * radius * (22.0/7);}

Defined outside class

Accessing Class MembersAccessing Class Members

Operators to access class membersOperators to access class members– Identical to those for Identical to those for structstructss– Dot member selection operator (Dot member selection operator (..))

ObjectObject Reference to objectReference to object

– Arrow member selection operator (Arrow member selection operator (->->) ) PointersPointers





void main(){ Circle c1,c2(7);

cout<<“The area of c1:” <<c1.getArea()<<“\n”;

//c1.raduis = 5;//syntax error c1.setRadius(5);

cout<<“The circumference of c1:”<< c1.getCircumference()<<“\n”;

cout<<“The Diameter of c2:”<<c2.getDiameter()<<“\n”;

}

The first constructor is

called

The second constructor is

called

Since radius is a private class data

member





void main(){ Circle c(7); Circle *cp1 = &c; Circle *cp2 = new Circle(7); cout<<“The are of cp2:”

<<cp2->getArea(); }

DestructorsDestructors

DestructorsDestructors– Special member functionSpecial member function– Same name as class Same name as class

Preceded with tilde (Preceded with tilde (~~))

– No arguments No arguments – No return valueNo return value– Cannot be overloadedCannot be overloaded– Before system reclaims object’s memoryBefore system reclaims object’s memory

Reuse memory for new objectsReuse memory for new objects Mainly used to de-allocate dynamic memory locationsMainly used to de-allocate dynamic memory locations

Another class ExampleAnother class Example

This class shows how to handle time parts.This class shows how to handle time parts.class Time{ private:

int *hour,*minute,*second; public:

Time();Time(int h,int m,int s);void printTime();void setTime(int h,int m,int s);int getHour(){return *hour;}int getMinute(){return *minute;}int getSecond(){return *second;}void setHour(int h){*hour = h;}void setMinute(int m){*minute = m;}void setSecond(int s){*second = s;}~Time();

};

Destructor

Time::Time(){

hour = new int;minute = new int;second = new int;*hour = *minute = *second = 0;

}

Time::Time(int h,int m,int s){

hour = new int;minute = new int;second = new int;*hour = h;*minute = m;*second = s;

}

void Time::setTime(int h,int m,int s){

*hour = h;*minute = m;*second = s;

}

Dynamic locations should be allocated

to pointers first

void Time::printTime(){ cout<<"The time is : ("<<*hour<<":"<<*minute<<":"<<*second<<")"

<<endl;}

Time::~Time(){

delete hour; delete minute;delete second;}

void main(){

Time *t;t= new Time(3,55,54);t->printTime();

t->setHour(7);t->setMinute(17);t->setSecond(43);

t->printTime();

delete t;}

Output:The time is : (3:55:54)The time is : (7:17:43)Press any key to continue

Destructor: used here to de-allocate memory locations

When executed, the destructor is called

Reasons for OOPReasons for OOP

1.1. Simplify programmingSimplify programming

2.2. InterfacesInterfaces Information hiding:Information hiding:

– Implementation details hidden within classes themselvesImplementation details hidden within classes themselves

3.3. Software reuseSoftware reuse Class objects included as members of other Class objects included as members of other

classesclasses

for(i=0;i<3;i++)for(i=0;i<3;i++) { { for(j=0;j<3;j++)for(j=0;j<3;j++) { { for(m=0;m<3;m++)for(m=0;m<3;m++) {{ X[i][j][m]=A[i][m]*B[m][j];X[i][j][m]=A[i][m]*B[m][j]; C[i][j]+=X[i][j][m];C[i][j]+=X[i][j][m]; }} }} }}

Class ActivityClass Activity

Write a program to computer an area of a Write a program to computer an area of a rectangle and triangle using the class rectangle and triangle using the class concept? concept?

ProjectProject http://www.micro-examples.com/public/microex-navig/doc/077-picobat.htmlhttp://www.micro-examples.com/public/microex-navig/doc/077-picobat.html

HowHow ? ? http://www.mikroe.com/eng/products/view/7/mikroc-pro-for-pic/

http://www.mikroe.com/eng/products/view/7/mikroc-pro-for-pic/

1 c++ structures starting to think about objects

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