一.求圆的周长

//
//  main.c
//  cdemo
//
//  Created by liyongkai on 2021/6/6.
//

#include <iostream>
using namespace std;

const double pi = 3.14;

class Cicle {
public:
    //成员属性  半径
    int m_r;
    
    //成员函数
    double calculate() {
        return  2 * pi * m_r;
    };
};


int main(int argc, const char * argv[]) {
    
    Cicle c;
    c.m_r = 10;
    cout << "c的周长为:" << c.calculate() << endl; //c的周长为:62.8
    
    return 0;
}

二.学生类

//
//  main.c
//  cdemo
//
//  Created by liyongkai on 2021/6/6.
//

#include <iostream>
using namespace std;

class Student {
public:
    string m_name;
    int m_id;
    
    void setName(string name) {
        m_name = name;
    }
    void setID(int ID) {
        m_id = ID;
    }
    
    void showInfo() {
        cout << "姓名:" << m_name <<"  "<< "学号:" << m_id << endl;
    }
};


int main(int argc, const char * argv[]) {
    
    Student std;
    std.setName("张三");
    std.setID(100);
    cout << "姓名:" << std.m_name <<"  "<< "学号:" << std.m_id << endl;
    //姓名:张三  学号:100
    
    std.showInfo();
    //姓名:张三  学号:100
    
    return 0;
}

三.