面向对象程序设计笔记

1.构造函数与析构函数

cout << Test::HelloStr << endl;     // 通过作用域运算符访问  
Test::HelloStr = "World";     // 修改静态变量 HelloStr  
Test t1;  
cout << t1.HelloStr <<endl;     // 通过对象访问  
Test::Hello();     // 通过作用域运算符访问  
t1.World();     // 通过对象访问  

class User{
	public:
		string Name;
		int Books=0;
		static int tot_books,tot_ren;
		User(string name,int books):Name(name),Books(books){
			cout<<Name<<" "<<Books<<" 进入"<<endl;
			tot_books+=Books;
			tot_ren++;
		};
		~User(){
			cout<<Name<<" "<<Books<<" 离开"<<endl;
			tot_books-=Books;
			tot_ren--;
		};
		static void GetState(){
			cout<<"书店人数:"<<tot_ren<<"，书店共享书数量:"<<tot_books<<"，人均共享数量:"
			<<tot_books/tot_ren<<endl;
		}
};
int User::tot_books=0;
int User::tot_ren=0;

2.内部类练习

/*  Cow a(weight,height);
    a.display(color);
    Cow::CowLeg leg(color, height);
    leg.show();                    */
class Cow{
    public:
        int weight,height;
        Cow(int _weight,int _height):weight(_weight),height(_height){};
        class CowLeg{
            public:
                string color;
                int length;
                CowLeg(string _color,int _length):color(_color),length(_length){};
                void display(string _color){
                    color=_color;
                }
                void show(){
                    cout<<"牛腿的颜色是"<<color<<endl;
                    cout<<"牛腿的长度是"<<length<<endl;
                }
        };
        CowLeg leg;
        ~Cow(){
            leg.show();
            cout<<"整牛高"<<height<<endl;
            cout<<"整牛重"<<weight<<endl;
        };   

3.类的书写（运算符重载）

3.1复数

class Complex{
	public:
		double real,image;
		Complex(double r,double i):real(r),image(i){};
		void Print(){
			if(image>=0) cout<<real<<"+"<<image<<"i"<<endl;
			else cout<<real<<image<<"i"<<endl;
		}
		Complex operator + (const Complex tem){
			return (Complex){real+tem.real, image+tem.image};
		} 
		Complex operator - (const Complex tem){
			return (Complex){real-tem.real, image-tem.image};
		} 
		Complex operator * (const Complex tem){
			//(a+bi)(c+di)=(ac-bd)+(ad+bc)i;
			return (Complex){real*tem.real-image*tem.image, real*tem.image+tem.real*image};
		} 
        Complex operator / (const Complex tem){
            double a=real,b=image,c=tem.real,d=tem.image;
			//(a+bi)(c-di)/(c^2+d^2)=[(ac+bd)+(bc-ad)i]/(c^2+d^2);
			return (Complex){(a*c+b*d)/(c*c+d*d),(b*c-a*d)/(c*c+d*d)};
		} 
};

4.友元函数与友元类

4.1友元函数

friend <返回类型> <函数名> (<参数列表>);  

class Test{  
    private:  
        int a;  
    protected:  
        int b;  
    public:  
        friend void fun(Test t);     // 友元函数  
};
void fun(Test t)  {  
    t.a = 100;  
    t.b = 2000;  
    cout << "a = " << t.a << ", b = " << t.b << endl;  
}
int main()  {  
    Test test;  
    fun(test);  
    return 0;  
}  

 4.2友元类

class TestFriend  {  
    private:  
        int a;  
};     // TestFriend 类的声明在 Test 类之前
class Test  {  
    private:  
        int a;  
        friend class TestFriend;     // 声明友元类  
};  

class TestFriend;     // 前置声明 TestFriend 类，只是一个名字
class Test  {  
    private:  
        int a;  
        friend class TestFriend;     // 声明友元类
        // 尝试将 TestFriend 类的成员函数 Func 作为友元函数，
        但由于 TestFriend 类目前只有前置声明，所以会出错。  
        friend void TestFriend::Func();     

};
class TestFriend     // TestFriend 类的声明在 Test 类之后  
{  
    private:  
        int a;  
    public:  
        void Func();  
};  

#include <iostream>
#include <string>
using namespace std;
class Teacher;
class Student{
	private:
		int number;
		string name,sex;
	public:
		Student(int num,string nam,string se):number(num),name(nam),sex(se){};
		void Print(){
			cout<<"学生："<<name<<"，编号："<<number<<"，性别："<<sex<<endl;
		}	
		friend class Teacher;
};

class Teacher{
	private:
		int number;
		string name,sex;
	public:
		void Print(){
			cout<<"教师："<<name<<"，编号："<<number<<"，性别："<<sex<<endl;
		}
		Teacher(const Student &a):number(a.number),name(a.name),sex(a.sex){};
};

4.3应用（矩阵）