1、Classes 2,Prepared by: Yang YongE-Mail:,Review questions,What is the difference between public members and private members? Please tell the difference between class and object. Do you think class is better than struct? How can you say that?,4. class A public: void setA(int); void showA() coutaendl;

2、private: int a; ; void setA(int x) a=x; ,#include void main() A B; int x; cinxendl; B. setA(x); coutB.aendl; ,Review questions,Contents,Constructor Copy-constructor Destructor Class combination Static members,Main objectives,How to define constructors and destructors for a class. Grasp the mechanism

3、 of class combination and the calling order in the class. How to use static members in the class.,Constructor,1.Definition: A special member function, it is primarily used to allocate memory for object and initialize the object as a particular state. 2. Characteristics: The name of constructor must

4、be same as the class name, or it will be regarded as a common member function. Recalled by the complier system automatically when the object is defined.,It can have any type of parameters, but cant have any returning type. So when defining and declaring a constructor, you cant point out its type, ev

5、en the “void” type. In practice, you usually need to define a constructor for each class. If you havent define a constructor, the complier will automatically create a constructor without a parameter. Its aim is to allocate a memory to the object.,Constructor,class A int a; public: void setA(int x) a

6、=x; void showA() coutaendl; ;,#include void main() A B; int x; coutx; B. setA(x); B.showA(); ,Example 1 of default constructor,A( ) ,class A int a; public: void setA(int x) a=x; void showA() coutaendl; ;,#include void main() A B; int x; coutx; B. setA(x); B.showA(); ,A( ) cout“Constructor”endl;,Exam

7、ple 2 of default constructor,Example of constructor,/ The declaration of constructor: class Clock public: Clock (int NewH, int NewM, int NewS); /constructor void ShowTime() coutHour“:” Minute “:” Second endl; private: int Hour,Minute,Second; ;,/The realization of constructor： Clock:Clock(int NewH, i

8、nt NewM, int NewS) Hour=NewH; Minute=NewM; Second=NewS; /The recall of constructor： void main() Clock A (10,10,15); /calling constructor A.ShowTime( ); ,Note: Constructor cant be recalled as other member functions, it must be recalled together with the object being defined: class_name object_name(pr

9、actical argument) The following is wrong： void main() Clock A; A. Clock(10,10,15); ,Example of constructor,Constructor with default parameters,For example: class simplecat public: simplecat(int age=0, int weight=0); int GetAge() return itsage; int GetWeight() return itsweight; private: int itsage; i

10、nt itsweight; ;,simplecat:simplecat(int age, int weight) itsage=age; itsweight=weight; void main() simplecat F1; coutF1.GetAge()tF1.GetWeight()endl; simplecat F2(5); coutF2.GetAge()tF2.GetWeight()endl; simplecat F3(5,8); coutF3.GetAge()tF3.GetWeight()endl; ,Copy-constructor,1. Definition: Copy-const

11、ructor is a special constructor, its format parameter is a reference of the self-class object. 2. Definition Method: class class_name public : class_name (formal argument)；/constructor class_name (class_name Copy-constructor only has a parameter, and the parameter must be the reference of self-class

12、 object; If the user hasnt defined a copy-constructor, you recall the default copy-constructor when defining a object.,Copy-constructor (cont.),Example of copy-constructor,class Point public: Point(int xx=0,int yy=0)X=xx; Y=yy; Point(Point,Point:Point (Point ,Destructor,1. Definition: Destructor is

13、a special member functions, and it performs opposite to the constructor, including the following tasks: Complete some cleaning work before the object being deleted. Automatically recall the destructor by the complier system when the survival period ended, and then free up all resource belonging to t

14、his object, such as memory space.,Destructor (cont.),2. Characteristics: The name of destructor is the same as constructor except with a “” before it; Destructor has no parameters and no returning value, and cant be overloaded. So there is only a destructor within a class. If destructor hasnt been d

15、eclared in the program, the complier will automatically create a default destructor.,Example of constructor and destructor,class demo int x,y; public: demo(int a, int b)x=a;y=b; demo(demo ,void main() demo d1; d1.show(); demo d2(3,5); d2.show(); ,Example of constructor and destructor,Example of clas

16、s application,一圓型游泳池如圖所示，現(xiàn)在需在其周?chē)ㄒ粓A型過(guò)道，并在其四周?chē)蠔艡?。柵欄價(jià)格為35元/米，過(guò)道造價(jià)為20元/平方米。過(guò)道寬度為3米，游泳池半徑由鍵盤(pán)輸入。要求編程計(jì)算并輸出過(guò)道和柵欄的造價(jià)。,游泳池,過(guò)道,#include const float PI = 3.14159; const float FencePrice = 35; const float ConcretePrice = 20; /Circle declarations class Circle private: float radius; public: Circle(float r); /con

17、structor float Circumference() ; / function for circumference float Area() ; / function for area ;,Circle:Circle(float r) radius=r; float Circle:Circumference() return 2 * PI * radius; float Circle:Area() return PI * radius * radius; ,Example of class application,void main() float radius; float Fenc

18、eCost, ConcreteCost; coutradius; / Declare two circles Circle Pool(radius); Circle PoolRim(radius + 3);,Example of class application,/ 計(jì)算柵欄造價(jià)并輸出 FenceCost = PoolRim.Circumference() * FencePrice; cout Fencing Cost is ￥ FenceCost endl; / 計(jì)算過(guò)道造價(jià)并輸出 ConcreteCost = (PoolRim.Area ( ) -Pool.Area()* Concret

19、ePrice; cout Concrete Cost is ￥ ConcreteCost endl; ,Overloading of constructors,Similar to a common function, the constructors also can be overloaded. The constructors which have similar function, but have different types and number of parameters, can be assigned to the same function name. The overl

20、oaded constructors can be respectively recalled according to their parameters types and number by the complier.,Example of overloaded constructors,class rectangle public: Rectangle( ); Rectangle(int width, int length); private: int width; int length; ; int main() Rectangle rect1; /call Rectangle( )

21、Rectangle rect2(4,5); /call Rectangle(int , int) ,Notes: When overloading the none-parameters constructors and constructors with default parameters, the main program will bring about duality.,For example: class rectangle public: Rectangle( ); Rectangle(int width=4, int length=6); private: int width;

22、 int length; ; int main() Rectangle rect1; Rectangle rect2(4,5); ;,The concept of class combination,The member data of one class is an object of another class. The more complicated abstract can be realized based on the existing abstract.,Example,class Point private: float x,y; public: Point(float h,

23、float v); float GetX(void); float GetY(void); void Draw(void); ; /.omit the realization of the functions,class Line private: Point p1,p2; public: Line (Point a,Point b); void Draw(void); ; /.omit the realization of the functions,Example,Class combination calling order,Recall order of constructors: F

24、irstly recall the constructor of built-in object. (According the order of declaration). Then recall the constructors of self-class. (The destructors recall order is to the contrary.) If recalling the default constructor ，the initialization of built-in object will recall the relevant default construc

25、tors simultaneously.,Example of class combination,#include int nextStudentID=0; class StudentID public: StudentID( ) value=+nextStudentID; cout Constructing StudentID:valueendl; StudentID() coutDestructing id:valueendl; protected: int value; ;,class Student public: Student(char * pName=“noName”) cou

26、t“Constructing student”“ ”pNameendl; Student()cout“Destructing Student” endl; protected: StudentID id; ; void main() Student s(“randy”); ,Constructor design of class combination,Principle： The constructor not only has to initialize fundamental type member data of self-class, but has to initialize th

27、e object member of other class. Declaration method： class:class(args.):object1(arg.)，object2(arg.)，. / initialization of the class. ,class StudentID public: StudentID(int id) value=id; coutAssigning student idvalueendl; StudentID( ) coutDestructing ID,valueendl; protected: int value; ;,class student

28、 public: student(char * pName=no name, int ssID=0):id(ssID) coutConstructing student,pName endl; protected: StudentID id; ;,void main() Student s(“Randy”,9818); student t(“Jenny”,9819); ,Constructor design of class combination,Former reference declaration,Class must be declared firstly before it can

29、 be used. If you want to cite some class before its being defined，your must use former reference declaration. Former reference declaration only to introduce an identifier for the program, and its detailed declaration is located somewhere else.,Example,class B; / former declaration class A public: vo

30、id f(B b); ; class B public: void g(A a); ;,Static member,1. Definition: Static member is similar to static variable. It doesnt belong to a certain object, but belongs to the whole class and shared by all objects of the class. Static member has two kinds: static member data, static member function.,

31、2. Static member data: Declared by keyword “static”. Used by all objects belonging to the class, so only updated once, all the static member data of all objects can be updated simultaneously, and its value is the same. Initialized outside of the class with: type classname: static data=initialization

32、 value,Static member (cont.),Example 1 of Static member data,#include class rectangle public: rectangle(int width=0, int length=0) itswidth=width; itslength=length; coutR+; rectangle(rectangle ,rectangle:rectangle(rectangle ,#include #include using namespace std; class Student string name; public: static int num; void set(string str) name = str; +num; ;,Example 2 of Static m