友元函数

#include <iostream>
using namespace std;

class Car
{
    friend void display(Car);
private:
    int speed;
    char color[20];
public:
    void input()
    {
        cout<<"Enter the speed:"<<endl;
        cin>>speed;
        cout<<"Enter the color:"<<endl;
        cin>>color;
    }
};

void display(Car x)//友元函数的定义
{
    cout<<"The speed of the car is:"<<x.speed<<endl;
    cout<<"The color of the car is:"<<x.color<<endl;
}

int main()
{
    Car mine;
    mine.input();
    display(mine);
    cout << "Hello World!" << endl;
    return 0;
}

#include <iostream>
using namespace std;

class Train;//提前声明 Train 是一个类

class Car
{
    friend void display(Car,Train);//友元函数
private:
    int speed;
    char color[20];
public:
    void input()
    {
        cout<<"Enter the speed of the car:"<<endl;
        cin>>speed;
        cout<<"Enter the color of the car:"<<endl;
        cin>>color;
    }
};

class Train
{
    friend void display(Car,Train);//友元函数
private:
    int speed;
    char color[20];
public:
    void input()
    {
        cout<<"Enter the speed of the train:"<<endl;
        cin>>speed;
        cout<<"Enter the color of the train:"<<endl;
        cin>>color;
    }
};

void display(Car c,Train t)//友元函数的定义
{
    if(c.speed>t.speed)
    {
        cout<<"The car is faster!!"<<endl;
        cout<<"The speed of the car is:"<<c.speed<<endl;
        cout<<"The color of the car is:"<<c.color<<endl;
    }
    else
    {
        cout<<"The train is faster!!"<<endl;
        cout<<"The speed of the train is:"<<t.speed<<endl;
        cout<<"The color of the train is:"<<t.color<<endl;
    }
}

int main()
{
    Car mine;
    mine.input();
    Train goverment;
    goverment.input();
    display(mine,goverment);
    return 0;
}

#include <iostream>
using namespace std;

class support
{
private:
    int x,y;
public:
    void init_add(int a,int b)
    {
        x=a;
        y=b;
    }
    friend class Add;
};

class Add
{
public:
    void add(support s)
    {
        cout<<s.x<<"+"<<s.y<<"="<<s.x+s.y<<endl;
    }
};

int main()
{
    support s;
    s.init_add(3,4);
    Add a;
    a.add(s);
    return 0;
}

#include <iostream>
#include <cstdlib>
using namespace std;

class A
{
private:
    int a;
    int b;
public:
    A(int x=0,int y=0):a(x),b(y){}
    A operator +(A &a1);
};

A A::operator +(A &a1)
{
    A a2;
    a2.a=this->a+a1.a;
    a2.b=this->b+a1.b;
    cout<<a2.a<<‘\t‘<<a2.b<<endl;
    return a2;
}

int main()
{
    A a1(5,6);
    A a2(7,8);
    A a3;
    a3=a1+a2;
    return 0;
}

#include <iostream>
#include <cstdlib>
using namespace std;

class complex
{
private:
    double real,imag;
public:
    complex(double,double);//初始化
    void show();//输出
    friend complex operator +(const complex &c1,const complex &c2);//友元函数运算符重载
};

inline complex::complex(double r1, double r2)//内联函数
{
    real=r1;
    imag=r2;
}

inline void complex::show()//内联函数
{
    cout<<‘(‘<<real<<‘,‘<<imag<<‘)‘<<endl;
}

complex operator +(const complex &c1,const complex &c2)
{
    complex c3(0,0);
    c3.real=c1.real+c2.real;
    c3.imag=c1.imag+c2.imag;
    return c3;
}

int main()
{
    complex c1(1.4,4.5),c2(3.4,5.7);
    complex c3=c1+c2;
    c3.show();
    return 0;
}