c++中继承和派生的问题。

Question

问题遇到的现象和发生背景

第23行的构造函数时的r为什么是yuan（r）这种形式，代表什么意思啊

问题相关代码，请勿粘贴截图

#include<iostream>
using namespace std;
class dian{
    public:
    virtual float min() = 0;
    virtual float tiji() = 0;
};
class yuan:public dian{
    float r;
    public:
    yuan(    float r){
    this->r=r; 
    }
    float min(){
        return 2*3.14*r; 
    }
    float tiji(){
        return 3.14*r*r;
    }
};
class yuanzu:public yuan{
    float r,h;
    public:    yuanzu(     float r,    float h1):yuan(r),h(h1){
    }
        float min(){yuan::min()*h;}
        float tiji(){return 0;} 
}; 
class sibianxing:public dian{
    float x,y;    
    public:
        
        sibianxing(     float x,    float y){
        this->x=x;
        this->y=y;
    }
     float min(){return x*y;}
        float tiji(){return 2*(x+y);}
}; 
class sifanti:public sibianxing {
    float x,y,h;
public:    sifanti(    float x,    float y,    float h1):sibianxing(x,y),h(h1){
    }
        float min(){return sibianxing::min()*h;}
        float tiji(){return 0;} 
}; 
int main()
{
    yuan a(2);
    yuanzu b(3,4);
    sibianxing c(4,5);
    sifanti d(1,2,3);
    cout<<"圆"<<a.min()<<","<<a.tiji()<<endl; 
    cout<<"圆柱"<<b.min()<<endl;
    cout<<"四边形"<<c.min()<<","<<c.tiji()<<endl;
    cout<<"四方体"<<d.min()<<endl;
    return 0;
}

运行结果及报错内容

我的解答思路和尝试过的方法

我想要达到的结果

Answer 1

初始化列表的固有写法。
调用顺序是：
1、成员变量的就地初始化
2、初始化列表
3、构造函数体