实验四

实验四

1.map的用法（实现键值对应）：

练习一：输入数字输出字母

#include<iostream>
#include<map>
#include<string>
int main(){
    using namespace std;
    map<int,string> trans{{0,"a"},
                          {1,"b"},
                          {2,"c"},
                          {3,"d"},
                          {4,"e"},
                          {5,"f"},
                          {6,"g"},
                          {7,"h"},
                          {8,"i"}} ;
    string a;
    while(cin>>a){
        for(auto i=0;i<a.length();i++)
        cout<<trans[a[i]-'0'];  
        cout<<"\n";
    }
}

 

练习二：实现十进制与任意进制数的转换

#include<iostream>
#include<string>
#include<vector>
#include<map> 
using namespace std;
void d2n(int n,int c=2){
    map<int,string> t={{10,"A"},{11,"B"},{12,"C"},{13,"D"},{14,"E"},{15,"F"}};
    vector<string> p;
    for(auto i=0;n!=0;i++){
        if(n%c>=10)
        p.push_back(t[n%c]);
        else{
        map<int,string> s={{0,"0"},{1,"1"},{2,"2"},{3,"3"},{4,"4"},{5,"5"},{6,"6"},{7,"7"},{8,"8"},{9,"9"}};
        p.push_back(s[n%c]);
        }
        n/=c;
    }    
    for(auto it=p.rbegin();it!=p.rend();it++)
    cout<<*it; 
    cout<<endl;
} 
int main()
{
    int  n,c;
    while(cin>>n)
    {
        cout<<"Default:";
        d2n(n);
        cout<<"Dec:\t";
        d2n(n,2);
        cout<<"Oct:\t";
        d2n(n,8);
        cout<<"Hex:\t";
        d2n(n,16);
    }
}

 

2.虚函数virtual

#include <iostream>
#include <typeinfo>

// definitation of Graph
class Graph
{
public:
    void draw() { std::cout << "Graph::draw() : just as an interface\n"; }
};


// definition of Rectangle, derived from Graph
class Rectangle : public Graph
{
public:
    void draw() { std::cout << "Rectangle::draw(): programs of draw a rectangle\n"; }
};


// definition of Circle, derived from Graph
class Circle : public Graph
{
public:
    void draw() { std::cout << "Circle::draw(): programs of draw a circle\n"; }
};


// definitaion of fun(): as a call interface
void fun(Graph *ptr)
{
    std::cout << "pointer type: " << typeid(ptr).name() << "\n";
    std::cout << "RTTI type: " << typeid(*ptr).name() << "\n";
    ptr -> draw();
}

// test 
int main()
{
    Graph g1;
    Rectangle r1;
    Circle c1;

    // call by object name
    g1.draw();
    r1.draw();
    c1.draw();

    std::cout << "\n";

    // call by object name, and using the scope resolution operator::
    r1.Graph::draw();
    c1.Graph::draw();

    std::cout << "\n";

    // call by pointer to Base class
    fun(&g1);
    fun(&r1);
    fun(&c1);
}

加上virtual后基类成员函数draw()变成了虚函数

#include <iostream>
#include <typeinfo>

// definitation of Graph
class Graph
{
public:
    virtual void draw() { std::cout << "Graph::draw() : just as an interface\n"; }//加上virtual 
};


// definition of Rectangle, derived from Graph
class Rectangle : public Graph
{
public:
    void draw() { std::cout << "Rectangle::draw(): programs of draw a rectangle\n"; }
};


// definition of Circle, derived from Graph
class Circle : public Graph
{
public:
    void draw() { std::cout << "Circle::draw(): programs of draw a circle\n"; }
};


// definitaion of fun(): as a call interface
void fun(Graph *ptr)
{
    std::cout << "pointer type: " << typeid(ptr).name() << "\n";
    std::cout << "RTTI type: " << typeid(*ptr).name() << "\n";
    ptr -> draw();
}

// test 
int main()
{
    Graph g1;
    Rectangle r1;
    Circle c1;

    // call by object name
    g1.draw();
    r1.draw();
    c1.draw();

    std::cout << "\n";

    // call by object name, and using the scope resolution operator::
    r1.Graph::draw();
    c1.Graph::draw();

    std::cout << "\n";

    // call by pointer to Base class
    fun(&g1);
    fun(&r1);
    fun(&c1);
}

两者运行结果如下：

 

 

 

3.车的类的继承与派生:

//battery.hpp
#include<iostream>
class Battery{
    public:
        Battery(double capacity0=70):capacity(capacity0){};
        double get_capacity()const{return capacity;}
    private:
        double capacity;
};
      

//car.hpp
#include<iostream>
#include<string>
using namespace std;
class Car{
    public:
        Car(string maker0,string model0,int year0,int odometers0=0):maker(maker0),model(model0),year(year0),odometers(odometers0){}
        Car()=default;
        void info()const;
        void update_odometers(int n);
    private:
    string maker,model;
    int year,odometers;
};
void Car::info()const{
    cout<<"maker:     \t"<<maker<<endl;
    cout<<"model：    \t"<<model<<endl;
    cout<<"year：     \t"<<year<<endl;
    cout<<"odometers：\t"<<odometers<<endl;
}
void Car::update_odometers(int n)
{
    if(n<odometers)
    cout<<"warning ,error number.."<<endl;
    else
    odometers=n;
    
}

//electricCar.hpp
#include<iostream>
#include<string>
#include"car.hpp"
#include"battery.hpp"
class ElectricCar:public Car{
    public:
        ElectricCar(string maker0,string model0,int year0,Battery battery0=70,int odometers0=0):Car(maker0,model0,year0,odometers0),battery(battery0){}
        ElectricCar()=default;
        void info ()const;
    private:
        Battery battery;
};
void ElectricCar::info()const{
    Car::info();
    cout<<"capacity:   \t"<<battery.get_capacity()<<endl;
}

//task.3
#include <iostream>
#include "electricCar.hpp"

int main()
{
    using namespace std;

    // test class of Car
    Car oldcar("dazhong", "a57", 2021);
    cout << "--------oldcar's info--------" << endl;
    oldcar.update_odometers(33);
    oldcar.info();

    cout << endl;

    // test class of ElectricCar
    ElectricCar newcar("benchi", "s5", 1988);
    newcar.update_odometers(0);
    cout << "\n--------newcar's info--------\n";
    newcar.info();
}

 

 

4.宠物类

//pets.hpp
#include<iostream>
#include<string>
using namespace std;
class MachinePets{
    public:
        MachinePets(const string s):nickname(s){}
        string get_nickname()const{return nickname;};
        virtual string talk() {return "gaga~";}
    private:
        string nickname;
};
class PetCats:public MachinePets{
    public:
        PetCats(const string s):MachinePets(s){}
        string talk(){return "miao wu~";};
};
class PetDogs:public MachinePets{
    public:
        PetDogs(const string s):MachinePets(s){}//构造函数要求与类的名称相同 
        string talk(){return "wang wang~";}
};

//task.4cpp
#include <iostream>
#include "pets.hpp"

void play(MachinePets *ptr)
{
    std::cout << ptr->get_nickname() << " says " << ptr->talk() << std::endl;
}

int main()
{
    PetCats cat("miku");
    PetDogs dog("da huang");

    play(&cat);
    play(&dog);
}

 

 实验总结：

这一次学习类的继承与派生，主要的作用是对代码的重用与扩充，非必要用到接口不使用，尽量用类的组合。

基类base,派生类derived,派生类对基类成员的访问权限依据两条原则：1.private成员不能被继承2.其余成员按权限小的定。

派生类的构造函数和析构函数：多重构造函数的调用顺序与（声明）的顺序有关。