C++类与对象

4.3Circle类 #include<iostream> using namespace std; //宏常量 const float PI=3.141593; const float FENCE_PRICE=35; const float CONCRETE_PRICE=20; //圆类 class Circle{ public: Circle(float r);//构造函数 float circumference();//成员函数计算周长 float area();//计算面积 private://私有成员 float radius; }; //类中成员函数的实现 Circle::Circle(float r){ radius=r; } float Circle::circumference(){ return 2*PI*radius; } float Circle::area(){ return PI*radius*radius; } int main(){ float radius; cout<<"Enter the radius of the pool:"; cin>>radius; Circle pool(radius);//边界对象 Circle poolRim(radius+3);//栅栏对象 float fenceCost=poolRim.circumference()*FENCE_PRICE; cout<<"Fencing Cost is $"<<fenceCost<<endl; float concreteCost=(poolRim.area()-pool.area())*CONCRETE_PRICE; cout<<"Concerte COst is $"<<concreteCost<<endl; return 0; } //构建了一个圆类，初始化了两个对象，并且分别调用了各个对象的成员函数，用其私有变量计算出所需的值

4.4类的组合

#include<iostream> #include<cmath> using namespace std; class Point{ public: Point(int xx=0,int yy=0){ x=xx; y=yy; cout<<"Calling the constructor of Point "<<endl; } Point(Point &p); int getX(){return x;} int getY(){return y;} private: int x,y; }; Point::Point(Point &p){ x=p.x; y=p.y; cout<<"Calling the copy constructor of Point"<<endl; } //类的组合,由point类组合而成的line类 class Line{ public: Line(Point xp1,Point xp2); Line(Line &l); double getLen(){return len;} private: Point p1,p2; double len;//线段的长度由构造函数计算得出 }; Line::Line(Point xp1,Point xp2):p1(xp1),p2(xp2){//p1=xp1,p2=xp2 cout<<"Calling constructor of Line"<<endl; double x=static_cast<double>(p1.getX()-p2.getX());//static_cast<double>将后面的表达式强制转换成double类型 double y=static_cast<double>(p1.getY()-p2.getY()); len=sqrt(x*x+y*y); } Line::Line(Line &l):p1(l.p1),p2(l.p2){ cout<<"Calling the copy constructor of Line"<<endl; len=l.len; } main(){ Point myp1(1,1),myp2(4,5); Line line(myp1,myp2); Line line2(line); cout<<"The length of the line is :"; cout<<line.getLen()<<endl; cout<<"The lenth of line2 is:"; cout<<line2.getLen()<<endl; } 4.7结构体

#include<iostream> #include<iomanip> #include<string> using namespace std; struct Student{ int num; string name; char sex; int age; }; main(){ Student stu={97001,"Lin Lin",'F',19}; cout<<"Num: "<<stu.num<<endl; cout<<"Name: "<<stu.name<<endl; cout<<"Sex: "<<stu.sex<<endl; cout<<"Age: "<<stu.sex<<endl; } //结构体和类的区别： //结构体是特殊的类，默认成员为公有类型，而类为私有 //C++引入结构体是为了保持和C语言的兼容性

4.8结构体作为类的成员变量

#include<string> #include<iostream> using namespace std; class ExamInfo{ public: //三种构造函数 ExamInfo(string name,char grade):name(name),mode(GRADE),grade(grade){} ExamInfo(string name,bool pass):name(name),mode(PASS),pass(pass){} ExamInfo(string name,int percent):name(name),mode(PERCENTAGE),percent(percent){} void show(); private: string name; enum{ GRADE, PASS, PERCENTAGE }mode;//记分方式 union{ char grade; bool pass; int percent; }; }; void ExamInfo::show(){ cout<<name<<":"; switch(mode){ case GRADE:cout<<grade; break; case PASS: cout<<(pass?"PASS":"FALL"); break; case PERCENTAGE: cout<<percent; break; } cout<<endl; } int main(){ ExamInfo course1("English",'B'); ExamInfo course2("Calculus",true); ExamInfo course3("C++Programming",85);//根据不同的数据类型调用不同的构造函数，自动产生不同的mode值 course1.show(); course2.show(); course3.show(); return 0; }

5.3

#include<iostream> using namespace std; class point { public: point (int x = 0, int y = 0):x(x),y(y){ count++; } point (point &p){ x = p.x; y = p.y; count++; } ~point(){count--;} int getX(){ return x; } int getY(){return y;} void showCount(){cout<<count<<endl;} private: int x,y; static int count; }; int point::count = 0; int main(){ point a(4,5); cout<<a.getX()<<a.getY()<<endl; a.showCount(); point b(a); b.showCount(); return 0; } #include<iostream> using namespace std; class point { public: point (int x = 0, int y = 0):x(x),y(y){ count++; } point (point &p){ x = p.x; y = p.y; count++; } ~point(){count--;} int getX(){ return x; } int getY(){return y;} static void showCount(){cout<<count<<endl;} private: int x,y; static int count; }; int point::count = 0; int main(){ point a(4,5); cout<<a.getX()<<a.getY()<<endl; point::showCount(); point b(a); point::showCount(); return 0; }