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Chapter - 4

Classes and Objects. Chapter - 4. Class. A class is a way to bind the data describing an entity and its associated functions together. In C++ class makes a data type that is used to create objects of this type. The Class Definition. class < class_name > { private : <variable declaration>;

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Chapter - 4

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  1. Classes and Objects Chapter - 4

  2. Class • A class is a way to bind the data describing an entity and its associated functions together. • In C++ class makes a data type that is used to create objects of this type.

  3. The Class Definition class <class_name> { private : <variable declaration>; <function declaration>; protected : <variable declaration>; <function declaration>; public : <variable declaration>; <function declaration>; };

  4. Class Method Definition • Outside the Class Definition return_type <class_name> :: <func_name> (parameter list) { : } Eg: class XYZ { private : int a; public : void enter( ); }; void XYZ ::enter ( ) { cin>>a; } • Inside the Class Definition class XYZ { private : int a; public : void enter( ) { cin>>a; } };

  5. Referencing Class Members • The members of class are referenced using object of the class. • Eg: for above class XYZ ob1.enter( );

  6. Arrays within the class • class Exarray { intarr[10]; public : int largest( void); int sum(void); };

  7. Scope of Class and Its members • Public Members : the data members and member functions are directly accessed by any function. • Private Members : the members are not accessible outside the class but accessible only by the member functions, and not inherited • Protected Members : the members are not accessible outside the class as Private members but are inherited to derived classes

  8. The scope rules and classes • Global Class • if a class definition occurs outside any function is called global class. • its object can be declared anywhere within the program. • Local Class • if a class definition occurs inside any other function is called local class • its object can not be declared anywhere in program.

  9. Global Vs. Local Object • If an object is declared outside any function then its called global object • While an object declared within another function then its called local class. • A global object can be declared only from global class • While a local object can be declared from a local class.

  10. Global Vs. Local Class class XYZ // global class { int a; public : void enter( ); }ob1; //global object void main ( ) { XYZ ob2; //local object : } void main ( ) { class XYZ //local class {int a; public : void enter( ); }ob1; //legal local object } void Func( ) { XYZ ob2; // illegal : }

  11. Types of Class Functions • Accessor Function: the function that allow user to access the data member of object but cannot change the value of data member. • Eg: class Student { intrno; public: Student( ) //Manager Function { rno=0; } void getrno( ) //Accessor Function { return rno; } void enter( ) //Mutator Function { cin>>rno; } }; • MutatorFunction:a member function that allows to change the data member of an object. • Manager Function : member function which initializes and destroying class objects.

  12. Nested Classes • A class declared within another class is called nested class or an object of one class declared inside another class is called Nested Class. • Eg: class X { : class Y { : }; }; Eg: Class X { ………. }; class Y { X ob1; };

  13. Inline Function • A function definition occurs inside the class definition • An inline function definition should be placed above all the functions that call it. • Are best for small functions which are called often. • Eg: class X { int a; public : inline void square( int I ) { cout<<I * I; } }; void main( ) { X ob1; ob1.square(5); : }

  14. Constant Member Function • If a member function of a class doesnot alter any data in the class then this member function may be declared as a constant member function using the keyword const. • Eg: int Maxi (int, int)const;

  15. Nesting of Member Functions • When a member function is called by another member function, it is called nesting of member functions.

  16. Memory allocation of objects • Member functions are created and placed in the memory space only once when the class is defined. • The memory space is allocated for objects’ data members only when the objects are declared. • No separate space is allocated for member functions when the objects are created. • Separate memory space is allocated to objects at the time of their declaration for their data members.

  17. Static Class Members • Static Data Member : its like a global variable which is globally available for all the objects of that class type. • A static data member must be defined outside the class definition. • Difference between Static & General Data member: • There is only one copy of this data member maintained for the entire class. • It is visible only within the class. • Static Member function: a member function that accesses only the static members of a class may be declared as static. Put static keyword before the function declaration in the class definition.

  18. Example: class X { static int count; : static void show( void ) { cout<<count; } : }; int X :: count;

  19. BOARD - 2011 Define a class Applicant in C++ with following description: • A data member Ano (Admission no) of type long • A data member Name of type String • A data member Agg (Aggregate Marks) of type float • A data member Grade of type char • A member function GradeMe( ) to find the Grade as per the Aggregate Marks obtained by a student. Equivalent Aggregate marks range and the respective Grades are shown as follows Aggregate marks Grade >= 80 A Less than 80 and >=65 B Less than 65 and >= 50 C Less than 50 and >=33 D Less than 33 E Public members: • A function Enter( ) to allow user to enter values for Ano, Name, Agg & call function GradeMe( )to find the Grade. • A function Result( ) to allow user to view the content of all the data members.

  20. class Applicant { long Ano; char Name[20 ]; float Agg; char Grade; void GradeMe( ) { if(Agg>=80) Grade = ‘A’; elseif( Agg>=65 && Agg<80 ) Grade = ‘B’; else if (Agg>=50 && Agg < 65) Grade = ‘C’; else if (Agg >=33 & Agg <50 ) Grade = ‘D’; else Grade = ‘E’; } Public : void Enter( ) {cout<<“Enter Ano;”; cin>>Ano; cout<<“Enter Name”; gets(Name); cout<<“Enter Aggregate marks”; cin>>Agg; GradeMe( ); } void Show( ) { cout<<Ano <<Name << Agg <<Grade; } };

  21. BOARD - 2010 Define a class STOCK in C++ with the following description: Private members : • Icode of type integer (Item Code) • Item of type string (Item Name) • Price of type float (Price of each item) • Qty of type integer (Quantity in stock) • Discount of type float (Discount % on the item) • A member function FindDisc( ) to calculate discount as per the following rule: if Qty < = 50 Discount is 0 if 50 < Qty <=100 Discount is 5 if Qty>100 Discount is 10 Public Members: • A function Buy( ) to allow user to enter values for ICode, Item, Price, Qty and call function FindDisc( ) to calculate the Discount. • A function ShowAll( ) to allow user to view the content of all the data members.

  22. class STOCK { private : intIcode; char Item[20]; flaot Price; int Qty; float Discount; void FindDisc( ) { if(Qty <=50) Discount = 0; else if(Qty >50 && Qty<=100) Discount = 5; else Discount = 10; } public : void Buy( ) { cout<<“Enter Icode”; cin>>Icode; cout<<“Enter Item’; gets(Item); cout<<“Enter Price”; cin>>Price; cout<<“Enter Qty”; cin>>Qty; FindDisc( ); } void ShowAll( ) { cout<<ICode << Item <<Price << Qty << Discount; } };

  23. BOARD - 2009 Define a class HOTEL in C++ with the following description: Private Members: Rno //Room No Name //Customer name Tariff //stores per day charges NOD //Number of days of stay Calc( ) // a function to calculate and return amount as NOD*Tariff and if NOD * Tariff is more than 10000 then as 1.05*NOD*Tariff Public members: checkin( ) // a function to enter the Rno, Name, Tariff and NOD checkout( ) // a function to display Rno, Name, Tariff, NOD and Amount by calling function CALC( )

  24. class HOTEL { intRno; char Name[20]; float Tariff; int NOD; float CALC( ) { if(NOD * Tariff > 10000 ) return 1.05*NOD*Tariff; else return NOD*Tariff; } public : void checkin( ) { cin>>Rno; gets(Name); cin>>Tariff; cin>>NOD; } void checkout( ) {cout <<Rno<<Name<<Tariff<<NOD; cout<<“Amount = “<<CALC( ); } };

  25. BOARD - 2008 Define a class Clothing in C++ with the following description Private members : Code of type string Type of type String Size of type integer Material of type String Price of type float A function Calc_Price( ) which calculates and assigns the value foGprice as follows: For the value of Material as “COTTON” Type Price (Rs) TROUSER 1500 SHIRT 1200 For material other than “COTTON” the above mentioned price gets reduced by 25% Public members : A constructor to assign initial values of Code, Type, and Material with the word “NOT ASSIGNED” and size and price with 0 A function ENTER( ) to input the values of the data members Code, Type, Size and Material and invoke the Calc_Price( ) function. A function Show( ) which displays the content of all the data members for a clothing.

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