构造函数使用代码：

#include <iostream>
using namespace std;
class Rec
{
   const int length;
   int width;
public:
   Rec():length(10){cout << "Rec无参构造函数" << endl;};
   Rec(int a,int b):length(a),width(b){cout << "Rec有参构造函数" << endl;};
   void set_length(int l);
   void set_width(int w);
   int get_length();
   int get_width();
   void show();
};


class Cir
{
    int &r;
public:
    Cir(int &a):r(a){cout << "Cir有参构造函数" << endl;};
    void set_r(int r);  //设置私有属性r的值
    void show(double PI=3.14);   //参数有默认值3.14
};


class Car  //类名首字母一般大小
{
    string color;
    string brand;
    int speed;
public:
    Car(){cout << "Car无参构造函数" << endl;};
    Car(string a,string b,int c):color(a),brand(b),speed(c){cout << "Car有参构造函数" << endl;};
    void set(string c,string b,int s);
    void display();
    void acc(int a);
};
int main()
{
    Rec a;
    int age=100;
    Rec b(age,22.2);
    int cc=8;
    Cir c(cc);
    Car s;
    Car ss("黑曜金","迈巴赫",200);
    Car *p=new Car[4];
}

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