CHAPTER 5 Class - Basic Concepts

Transcription

1 CHAPTER 5 Class - Basic Concepts Page 1

2 Procedural Languages (or) Traditional Languages (or) Structured Languages: The traditional way of programming (procedural programming) is action-oriented and the unit of the program is the function. In this kind of languages, there is no security for the data used in the program. Example: Pascal, BASIC and C languages. Object Oriented Programming (OOP) The Object-Oriented is the natural way of thinking and of writing computer programs. The unit of OOP is the object. Example: Smalltalk, C++, Java, C# C++: C++ is derived from the C language. Strictly speaking, it is the superset of C. Almost every correct statement in C is also a correct statement in C++, although the reverse is not true. C++ means, C=C+1. The one and only difference here in C++ is Class concept. So, C++ was originally called C with classes. OO Design Analyze the problem and determine what objects are needed. Determine what attributes the objects will need to have. Determine what behaviors (actions) the objects will need to exhibit. Specify how the objects will needs to interact with each other. Examples: Objects: man, animal, book, car, computer etc. Attributes: size, shape, color, weight etc. Behaviors (Actions): read, walk, sleep, move etc. Page 2

3 OOP Features (or) Characteristics 1) Natural way to view the programming process. 2) Encapsulation: Data and functions are combined into a single entity is called Encapsulation. Data (attributes)+functions (behaviors)=abstract Data Type (ADT). Thus the Encapsulation technique closely related to Data Abstraction and Data hiding. 3) Inheritance: The idea of deriving a new one from the existing one. Provides the idea of code reusability Example: cars, trucks, busses and motorcycles are derived from vehicles. 4) Polymorphism: One thing with several distinct forms. Overloading is a kind of polymorphism. Example: function overloading, operator overloading Class Class is a user-defined data type. It is a logical way of grouping data and functions in the same structure. They are declared using the keyword class. This is similar in functionality to that of the C language keyword struct, but with the possibility of including functions as members, instead of only data. Typically there are two steps to implement classes in a program. 1. Define the class. Normally, class is defined before the main() function. 2. Create objects of the class. Mostly, objects are created inside the main() function. Page 3

4 Class Definition General format of a class definition: class class-name access specifier: member1; member2; access specifier: member1; member2; ; class is a keyword followed by the class-name(may be any name given by user). Note: A semicolon is required after the closing brace of the class definition. Access specifiers: Specify the accessibility of the members of the class. These are keywords and should be typed in small letters. There are three kind of access specifiers used in class 1. private: Members (data or function) are accessible only to the function members of the same class or to their friend classes. The private member is inaccessible from outside the class Mostly data members are declared inside this access specifier to provide data hiding. Page 4

5 It is the default access specifier. Hence in the absence of any access specifiers, the members are considered to be private. 2. public: Members (data or functions) are accessible from anywhere the class is visible. (i.e., the program has access the object). Mostly function members are defined inside this access specifier. 3. protected: Same as private and will be discussed later. Example 1(Function members without scope resolution operator) class time private: int hour; int minutes; int seconds; public: void gettime() cout<<"enter the hour"<<endl; cin>>hour; cout<<"enter the minutes"<<endl; cin>>minutes; cout<<"enter the seconds"<<endl; cin>>seconds; ; void printtime() cout<<"the Time is"<<hour<<":"<<minutes<<":"<<seconds<<endl; Page 5

6 Function members can be defined outside the class by using the scope resolution operator (::). Thus the scope resolution operator(::) provides exactly the same scope properties as if it was directly defined within the class. Example 2(Function members with scope resolution operator) class time private: int hour; int minutes; int seconds; public: void gettime(); void printtime(); ; void time::gettime() cout<<"enter the hour"<<endl; cin>>hour; cout<<"enter the minutes"<<endl; cin>>minutes; cout<<"enter the seconds"<<endl; cin>>seconds; void time::printtime() cout<<"the Time is"<<hour<<":"<<minutes<<":"<<seconds<<endl; Note: Both methods having the same effect in the program. Most of the programmers are following the class definition as in the Example 2. Page 6

7 Object of the class: Like the structure variables, the class should have the variables to access its public members. Class variables are called as objects. An Object is said to be an instance (copy or blueprint) of a class. Example: For the above class time, the objects can be created like time t1,t2,*t; time t[10]; Accessing Public Members of a class: Public members of a class are accessed through the member access operators such as 1. The dot operator(.) 2. The arrow operator (->) Using dot (.) operator: Public members of a class are accessed through dot(.) operator, when the class variables(objects) are normal variables. Example Program: #include<iostream> using namespace std; class time private: int hour; int minutes; int seconds; public: void gettime(); void printtime(); ; void time::gettime() cout<<"enter the hour"<<endl; cin>>hour; cout<<"enter the minutes"<<endl; Page 7

8 cin>>minutes; cout<<"enter the seconds"<<endl; cin>>seconds; void time::printtime() cout<<"the Time is"<<hour<<":"<<minutes<<":"<<seconds<<endl; int main() time t1,t2; t1.gettime(); t1.printtime(); t2.gettime(); t2.printtime(); return(0); Output: Enter the hour 10 Enter the minutes 12 Enter the seconds 34 The Time is10:12:34 Enter the hour 6 Enter the minutes 55 Enter the seconds 9 The Time is6:55:9 Page 8

9 Note: Public members are accessible through the objects. Private members are accessible only inside the public members. Accessing private members of a class through objects are violating the concept of data hiding. It is not allowed. t1.hour, t1.minutes and t1.seconds are illegal access. Using arrow (->) operator: Public members of a class are accessed through arrow(->) operator, when the class variables(objects) are pointer variables. Example Program: #include<iostream> using namespace std; class time private: int hour; int minutes; int seconds; public: void gettime(); void printtime(); ; void time::gettime() cout<<"enter the hour"<<endl; cin>>hour; cout<<"enter the minutes"<<endl; cin>>minutes; cout<<"enter the seconds"<<endl; cin>>seconds; Page 9

10 void time::printtime() cout<<"the Time is"<<hour<<":"<<minutes<<":"<<seconds<<endl; int main() time t1,*t2; t2=&t1; t1.gettime(); t2->printtime(); return(0); Output: Enter the hour 8 Enter the minutes 51 Enter the seconds 27 The Time is8:51:27 Initializing Class Objects: (Constructors) Data members cannot be initialized where they are declared in the class body. These should be initialized by the special member function, which is called constructor. Constructor Is a special member function with the same name as the class Initializes the data members of a class object is called automatically when an object is created Has no return type. Page 11

11 Example: For the above class time create two objects t1, t2 then initialize the object t1 with hour=5, minutes=10 and seconds=15. #include<iostream> using namespace std; class time private: int hour; int minutes; int seconds; public: time(); time(int,int,int); void gettime(); void printtime(); ; time::time(int h,int m,int s) hour=h; minutes=m; seconds=s; time::time() void time::gettime() cout<<"enter the hour"<<endl; cin>>hour; Page 11

12 cout<<"enter the minutes"<<endl; cin>>minutes; cout<<"enter the seconds"<<endl; cin>>seconds; void time::printtime() cout<<"the Time is"<<hour<<":"<<minutes<<":"<<seconds<<endl; int main() time t1(5,10,15),t2; t1.printtime(); t2.gettime(); t2.printtime(); return(0); Output: The Time is5:10:15 Enter the hour 9 Enter the minutes 12 Enter the seconds 39 The Time is9:12:39 Using Default Arguments with Constructors We can use the default arguments with constructors, when the objects get initialized with default values. Example: Page 12

13 For the above class time, create five objects t1, t2, t3, t4 and t5. The constructor function have hour=10, minutes=10 and seconds=10 as the default values. Initialize the object t1 with these default values. Initialize the object t2 with hour=9. Initialize the object t3 with hour=6 and minutes=14. Initialize the object t4 with hour=12, minutes=25 and seconds=44. Get the value for t5 with gettime() function and print all the time with printtime() function. #include<iostream> using namespace std; class time private: int hour; int minutes; int seconds; public: time(int=10,int=10,int=10); void gettime(); void printtime(); ; time::time(int h,int m,int s) hour=h; minutes=m; seconds=s; void time::gettime() cout<<"enter the hour"<<endl; cin>>hour; cout<<"enter the minutes"<<endl; Page 13

14 cin>>minutes; cout<<"enter the seconds"<<endl; cin>>seconds; void time::printtime() cout<<"the Time is"<<hour<<":"<<minutes<<":"<<seconds<<endl; int main() time t1,t2(9),t3(6,14),t4(12,25,44),t5; t5.gettime(); t1.printtime(); t2.printtime(); t3.printtime(); t4.printtime(); t5.printtime(); return(0); Output: Enter the hour 12 Enter the minutes 12 Enter the seconds 12 The Time is10:10:10 The Time is9:10:10 The Time is6:14:10 The Time is12:25:44 The Time is12:12:12 Page 14

15 Passing Objects to Functions Objects may be passed as arguments to the functions and also returned from functions. Example: Read two distance d1, d2 in the form of feet and inches by using a class distance. Add these two distances and return the result to another distance d3. Hint: 1 feet=12 inches #include<iostream> using namespace std; class dist private: int feet; float inches; public: dist(); void getdist(); void showdist(); dist adddist(dist); ; dist::dist() feet=0; inches=0.0; void dist::getdist() cout<<"enter the feet"<<endl; cin>>feet; cout<<"enter the inches"<<endl; cin>>inches; Page 15

16 dist dist::adddist(dist d2) dist temp; temp.inches=inches+d2.inches; if(temp.inches>=12.0) temp.inches=temp.inches-12; temp.feet=1; temp.feet=temp.feet+feet+d2.feet; return(temp); void dist::showdist() cout<<feet<<"\'-"<<inches<<"\""<<endl; int main() dist d1,d2,d3; d1.getdist(); d2.getdist(); d3=d1.adddist(d2); cout<<"distance1 is"; d1.showdist(); cout<<"distance2 is"; d2.showdist(); cout<<"distance3 is"; d3.showdist(); return(0); Page 16

17 Output: Enter the feet 34 Enter the inches 11 Enter the feet 56 Enter the inches 10 Distance1 is34'-11" Distance2 is56'-10" Distance3 is91'-9" Exercises: 1. Write a C++ program to get 2 dates and print the dates by using a class date. 2. Write a C++ program to calculate the area and circumference of a circle by using a class circle. 3. Write a C++ program to create two dates by using a class date. Initialize one date with day=4, month=7 and year=1977. Read another date through getdate() function and print both dates by printdate() function. 4. Write a C++ program to create five dates d1, d2, d3, d4 and d5 for the class date. The constructor function have day=10, month=5 and year=1978 as the default values. Initialize the object d1 with these default values. Initialize the object d2 with day=12. Initialize the object d3 with day=25 and month=11. Initialize the object d4 with day=7, month=10 and year=2005. Get the value for d5 with getdate() function and print all the dates with printdate() function. Page 17

18 5. Create a class Rectangle with length and breadth as private data members and also provide the following member functions: getdata(): gets the length and breadth of rectangle. calarea(): return the area of the rectangle. calperi(): return the perimeter of the rectangle. issquare(): return true if the rectangle is square. 6. Write a C++ program to read two lengths l1, l2 in the form of meters and centimeters by using a class length. Add these two lengths and return the result to another length l3. Hint: 1 meter=100 centimeters 7. Write a C++ program to read real and imaginary part of two complex numbers c1 and c2 by using class complex. Add these two complex numbers and return the result to another complex number c3. Page 18

19 CHAPTER 6 Class-Advanced Concepts - Inheritance Page 1

20 Introduction: The idea of deriving a new class from the existing class. Provides the idea of code reusability. Existing class is called as base class (or) super class. Derived class is called as sub class. Derived class inherits the data members and member functions from the previously defined base class. The idea of inheritance implements the is a relationship. For example, mammal IS-A animal, dog IS-A mammal hence dog IS-A animal as well and so on. Example: Base class Student Shape Loan Employee Account Derived classes GraduateStudent UndergraduateStudent Circle Triangle Rectangle CarLoan HomeImprovementLoan MortgageLoan FacultyMember StaffMember CheckingAccount SavingsAccount Types of Inheritance 1. Single Inheritance - One base class and one derived class. Base class Sub class Page 2

21 2. Multiple Inheritance - A class is derived from more than one base classes Base class1 Base class 2 Sub class 3. Multilevel Inheritance - A sub class inherits from a class which inherits from another class. Base class Sub class 1 Sub class 2 4. Hierarchical Inheritance - More than one sub class inherited from a single base class. Base class Sub class 1 Sub class 2 Sub class 3 Note: A class can be derived from more than one class, which means it can inherit data and functions from multiple base classes. Page 3

22 Access Control and Inheritance: A derived class can access all the non-private members of its base class. Thus base-class members that should not be accessible to the member functions of derived classes should be declared private in the base class. We can summarize the different access types according to who can access them in the following way: Access specifier (versus) Limits Public Protected Private Within the Same Class Derived Yes Yes Yes Yes Yes No Classes Outside of Classes Yes No No A derived class inherits all base class functions with the following exceptions: 1. Constructors, destructors and copy constructors of the base class. 2. Overloaded operators of the base class. 3. The friend functions of the base class. Mode of Deriving a class from Base Class: A class can be derived from base class in three modes of access specifiers. The general format of derived class from base is: class derived-class:access-specifier base-class.. ;

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24 Where access-specifier is one of public, protected, or private, and base-class is the name of a previously defined class. If the access-specifier is not used, then it is private by default. While using different modes of access specifiers, following rules are applied: 1. Public Mode: When deriving a class in a public mode, public members of the base class become public members of the derived class protected members of the base class become protected members of the derived class. A base class's private members are never accessible directly from a derived class, but can be accessed through calls to the public and protected members of the base class. 2. Protected Mode: When deriving a class in protected mode, public and protected members of the base class become protected members of the derived class. 3. Private Mode: When deriving a class in a private mode, public and protected members of the base class become private members of the derived class. Note: We hardly use protected or private modes of access speficiers, but public mode access specifier is commonly used. Base Class member (versus) Mode of Private Protected Public Derivation Private Inaccessible Private Private Protected Inaccessible Protected Protected Public Inaccessible Protected Public Page 5

25 It is the time to introduce the concept of protected access specifier. protected: Intermediate level of protection between private and public access specifies. Derived-class members can refer to public and protected members of the base class simply by using the member names Note that protected data breaks encapsulation Note: When you derive the sub class from the base class in public mode, specify the base class data members as protected members. The protected members are accessible in derived class. But the private members are not accessible. This is the only difference between the private and protected access specifiers. Single Inheritance: With Public mode of derived class Example Program: Write a C++ program to implement the single inheritance on the classes Shape and Rectangle. Derive the class Rectangle from the class Shape in public mode. The class Shape consists of length and breadth as data members and getdata() as a member function to get the length and breadth. The derived class Rectangle consists of area and perimeter as data members and calculate() as a member function to calculate the area and perimeter, issquare() as a member function to check the rectangle is square or not, display() as a member function to display the information of Rectangle. Page 6

26 Program: #include<iostream> using namespace std; //Base class class shape protected: float length; float breadth; public: void getdata(); ; Shape Rectangle void shape::getdata() cout<<"enter the length of shape"<<endl; cin>>length; cout<<"enter the breadth of shape"<<endl; cin>>breadth; //Derived class class rect:public shape private: float area; float peri; public: void calculate(); void display(); void issquare(); ; Page 7

27 void rect::calculate() area=length*breadth; peri=2*(length+breadth); void rect::issquare() if(length==breadth) cout<<"rectangle is square"<<endl; else cout<<"rectangle is not square"<<endl; void rect::display() cout<<"length of the Rectangle is:"<<length<<endl; cout<<"breadth of the Rectangle is:"<<breadth<<endl; cout<<"area of the Rectangle is:"<<area<<endl; cout<<"perimeter of the Rectangle is:"<<peri<<endl; int main() rect a; a.getdata(); a.calculate(); a.issquare(); a.display(); return(0); Page 8

28 Output: Enter the length of shape 12.3 Enter the breadth of shape 34.5 Rectangle is not square Length of the Rectangle is:12.3 Breadth of the Rectangle is:34.5 Area of the Rectangle is: Perimeter of the Rectangle is:93.6 Hierarchical Inheritance: With Public mode of derived class Example Program: Write a C++ program to implement the hierarchical inheritance on the classes Shape, Rectangle and Triangle. Derive the classes Rectangle and Triangle from the class Shape in public mode. The class Shape consists of side1 and side2 as data members and getdata() as a member function to get these sides. The derived class Rectangle consists of area as a data member and calarea() as a member function to calculate the area, display() as a member function to display the information of Rectangle. The derived class Triangle consists of area as a data member and calarea() as a member function to calculate the area, display() as a member function to display the information of Triangle. Page 9

29 Program: #include<iostream> using namespace std; Shape //Base class class shape protected: float side1; Rectangle Triangle float side2; public: void getdata(); ; void shape::getdata() cout<<"enter the side1 of your shape"<<endl; cin>>side1; cout<<"enter the side2 of your shape"<<endl; cin>>side2; //Derived class 1 class rect:public shape private: float area; public: void calarea(); void display(); ; Page 11

30 void rect::calarea() area=side1*side2; void rect::display() cout<<"length of the Rectangle is:"<<side1<<endl; cout<<"breadth of the Rectangle is:"<<side2<<endl; cout<<"area of the Rectangle is:"<<area<<endl; //Derived class 2 class tri:public shape private: float area; public: void calarea(); void display(); ; void tri::calarea() area=(side1*side2)/2; void tri::display() cout<<"base of the Triangle is:"<<side1<<endl; cout<<"height of the Rectangle is:"<<side2<<endl; cout<<"area of the Triangle is:"<<area<<endl; Page 11

31 int main() rect a; tri b; a.getdata(); a.calarea(); a.display(); b.getdata(); b.calarea(); b.display(); return(0); Output: Enter the side1 of your shape 1223 Enter the side2 of your shape 3323 Length of the Rectangle is:12.3 Breadth of the Rectangle is:33.7 Area of the Rectangle is: Enter the side1 of your shape 3.23 Enter the side2 of your shape 1321 Base of the Triangle is:34.5 Height of the Rectangle is:17.8 Area of the Triangle is: Page 12

32 Multiple Inheritance: With Public mode of derived class Example Program: Write a C++ program to implement the multiple inheritance on the classes Person, Employee and Teacher. Derive the class Teacher from two base classes Person and Employee in public mode. The Base class Person consists of name, age and sex as data members and getperson() as a member function to get these information. Another Base class Employee consists of Employee ID(EID), Basic Pay(BP), Human Resource Allowance(HRA), Dearness Allowance(DA) and Provident Fund(PF) as data members and getemp() as a member function to get the above information, calsalary() as a member function to calculate the Net Pay(NP=BP+HRA+DA-PF). The derived class Teacher consists of Designation, Years of Teaching Experience(YTE), Years of Industrial Experience(YIE), Total Experience(TE) as data members and getteach() as a member function to get these information, caltotexp() as a member function to calculate the Total Experience(TE=YTE+YIE), display() as a member function to display all the information of Teacher. Page 13

33 Program: #include<iostream> using namespace std; //Base class 1 class person Person Employee protected: char name[30]; int age; char sex[5]; public: Teacher void getperson(); ; void person::getperson() cout<<"enter the Name of the Person"<<endl; cin>>name; cout<<"enter the age of the Person"<<endl; cin>>age; cout<<"enter the sex of the Person"<<endl; cin>>sex; //Base Class 2 class employee protected: int eid; float bp,hra,da,pf,np; public: void getemp(); void calsal(); void display(); ; Page 14

34 void employee::getemp() cout<<"enter the Employee ID"<<endl; cin>>eid; cout<<"enter Basic Pay of Employee"<<endl; cin>>bp; cout<<"enter Human Resource Allowance of Employee"<<endl; cin>>hra; cout<<"enter Dearness Allowance of Employee"<<endl; cin>>da; cout<<"enter Provident Fund of Employee"<<endl; cin>>pf; void employee::calsal() np=bp+hra+da-pf; //Derived class class teacher:public person, public employee private: char des[20]; int yte; int yie; int te; public: void getteach(); void caltotexp(); void display(); ; Page 15

35 void teacher::getteach() cout<<"enter the Designation of the Teacher"<<endl; cin>>des; cout<<"enter the Years of Teaching Experience"<<endl; cin>>yte; cout<<"enter the Years of Industrial Experience"<<endl; cin>>yie; void teacher::caltotexp() te=yte+yie; void teacher::display() cout<<"name of the Teacher is:"<<name<<endl; cout<<"age of the Teacher is:"<<age<<endl; cout<<"sex of the Teacher is:"<<sex<<endl; cout<<"employee ID of the Teacher is:"<<eid<<endl; cout<<"basic Pay of the Teacher is:"<<bp<<endl; cout<<"human Resource Allowance of the Teacher is:"<<hra<<endl; cout<<"dearness Allowance of the Teacher is:"<<da<<endl; cout<<"provident Fund of the Teacher is:"<<pf<<endl; cout<<"net Pay of the Teacher is:"<<np<<endl; cout<<"designation of the Teacher is:"<<des<<endl; cout<<"years of Teaching Experience of the Teacher is:"<<yte<<endl; cout<<"years of Industrial Experience of the Teacher is:"<<yie<<endl; cout<<"years of Total Experience of the Teacher is:"<<te<<endl; Page 16

36 int main() teacher t; t.getperson(); t.getemp(); t.calsal(); t.getteach(); t.caltotexp(); t.display(); return(0); Output: Enter the Name of the Person Ahmed Enter the age of the Person 35 Enter the sex of the Person male Enter the Employee ID Enter Basic Pay of Employee Enter Human Resource Allowance of Employee Enter Dearness Allowance of Employee Enter Provident Fund of Employee Enter the Designation of the Teacher Lecturer Enter the Years of Teaching Experience 12 Enter the Years of Industrial Experience 3 Page 17

37 Name of the Teacher is:ahmed Age of the Teacher is:35 Sex of the Teacher is:male Employee ID of the Teacher is: Basic Pay of the Teacher is: Human Resource Allowance of the Teacher is: Dearness Allowance of the Teacher is: Provident Fund of the Teacher is: Net Pay of the Teacher is: Designation of the Teacher is:lecturer Years of Teaching Experience of the Teacher is:12 Years of Industrial Experience of the Teacher is:3 Years of Total Experience of the Teacher is:15 Exercise: 1. In the example program of multiple inheritance, change the name of getperson() function as getdata(), getemp() function as getdata() and getteach() function as getdata(), and then execute the program. What is the change you find in the output of the program? What is this concept is called in OOPs? Clarify the details. Page 18

38 CHAPTER 7 Class-Advanced Concepts - Polymorphism Page 1

39 Polymorphism: In object-oriented programming, polymorphism is a generic term that means 'many forms'. (From the Greek meaning "having multiple forms"). There are two types of polymorphism: 1. Compile time polymorphism Examples: function overloading, operator overloading 2. Run time polymorphism: Examples: virtual functions. Operator Overloading: C++ allows you to redefine how standard operators work when used with class objects. For example, the operator + is used to add two integer or floating point values. This is the nature of + operator. But by overloading the + operator, we can add two objects in C++. Let us consider int a=10; int b=15; int c=a+b; Thus the operator + is used to add two variables of type int or float. Is this possible to add two objects of class? Yes, it s possible by operator overloading concept. Let us consider the following class class complex float r; float img; ; Page 2

40 complex c1,c2,c3; By using operator overloading concept we can add two complex numbers and store the result to another object. i.e; c3=c1+c2; Here for the operator+ function, the right side object c2 is passed as an argument. Note: In C++ some of the operators are cannot be overloaded. They are?:..* :: sizeof The general format of operator overloading function prototype is returntype operatorsymbol(parameter for object on the right side of operator); Note: here operator is a keyword Example: void operator<<( parameter for object on the right side of operator); complex operator+( complex); distance operator-(complex); circle operator/(circle); Example Program: Write a C++ program to read real and imaginary part of two complex numbers c1 and c2 by using class complex. Add these two complex numbers by overloading the + operator and then return the result to another complex number c3. Page 3

41 #include<iostream> using namespace std; class complex private: float r; float img; public: void getdata(); void print(); complex operator+(complex); ; void complex::getdata() cout<<"enter the real part"<<endl; cin>>r; cout<<"enter the imaginary part"<<endl; cin>>img; void complex::print() cout<<r<<"+"<<img<<"j"<<endl; complex complex::operator+(complex z) complex temp; temp.r=r+z.r; temp.img=img+z.img; return(temp); Page 4

42 int main() complex c1,c2,c3; c1.getdata(); c2.getdata(); cout<<"the first complex number is"<<endl; c1.print(); cout<<"the second complex number is"<<endl; c2.print(); c3=c1+c2; cout<<"the result of addition is"<<endl; c3.print(); return(0); Output: Enter the real part 11.2 Enter the imaginary part 4.5 Enter the real part 22.1 Enter the imaginary part 5.6 The first complex number is j The second complex number is j The result of addition is j Page 5

43 Friends of Classes: A friend is a function or class that is not a member of class, but has access to the private and protected members of the class. friend function and friend classes Can access private and protected members of another class friend functions are not member functions of a class Defined outside of class scope Properties of friendship Friendship is granted, not taken Not symmetric (if B a friend of A, A not necessarily a friend of B) Not transitive (if A a friend of B, B a friend of C, A not necessarily a friend of C) friend declarations 1. To declare a friend function Type friend before the function prototype (declaration) in the class that is giving friendship friend returntype functionname(parameterstype); should appear in the class giving friendship 2. To declare a friend class Type friend class classname in the class that is giving friendship if class A is granting friendship to class B, then friend class B; should appear in class A's definition Example Program (Friend Function) Create a class rectangle with length and breadth as private data members and also provide the following member functions: getdata(): gets the length and breadth of rectangle. calarea(): return the area of the rectangle. and write a function issquare() as a friend of class rectangle which gets a rectangle as an argument and return true if the rectangle is square. Page 6

44 Program: #include<iostream> using namespace std; class rect private: float l; float b; float area; public: void getdata(); float calarea(); friend bool issquare(rect); ; void rect::getdata() cout<<"enter the length"<<endl; cin>>l; cout<<"enter the breadth"<<endl; cin>>b; float rect::calarea() area=l*b; return(area); Page 7

45 bool issquare(rect x) if(x.l==x.b) return(true); else return(false); int main() rect r; float res1; bool res2; r.getdata(); res1=r.calarea(); cout<<"the area is"<<res1<<endl; res2=issquare(r); if(res2==1) cout<<"the rectangle is square"<<endl; else cout<<"the rectangle is not square"<<endl; return(0); Page 8

46 Output: Enter the length 12.3 Enter the breadth 5.6 The area is68.88 The rectangle is not square Exercises: 1. Write a C++ program to read real and imaginary part of two complex numbers c1 and c2 by using class complex. Subtract c2 from c1 by overloading the - operator and then return the result to another complex number c3. 2. Write a C++ program to read two distance d1, d2 in the form of feet and inches by using a class distance. Add these two distances by overloading the + operator and return the result to another distance d3. Hint: 1 feet=12 inches Page 9