Learning of C++ classes and objects [part1: encapsulation]

Learning of C++ classes and objects [part1: encapsulation]

Attributes and behavior as a whole

From here, we will explore the topic of classes. The three elements of classes are encapsulation-inheritance-polymorphism.
Let's start with the package.
Refer to the following code:

// arrayone.cpp -- small arrays of integers
#include <iostream>

using namespace std;

const double PI = 3.14;

//要设计一个类
class Circle
{
    
    
    //访问权限
    //公共权限
public:
    //属性（通常为变量）
    int radius;

    //行为（通常为函数）
    //获取圆的周长
    double calculate()
    {
    
    
        return 2 * PI * radius;
    }
};

int main()
{
    
    
    //通过圆类创建具体对象（实例化）
    Circle c1;
    //为圆对象属性赋值
    c1.radius = 10;

    cout << "圆的周长为" << c1.calculate() << endl;

    system("pause");
    return 0;
}

Here we have created a circle class and calculated its perimeter based on its radius. The code is very simple and will not be repeated.
Professional terms that need attention:

• The attributes and behaviors in the class are collectively called members
• Attribute is also called member attribute member variable
• Behavior is also called member function member method

Why do members of the class like to add an m_ or end with _?
In order to prevent the following situations:

name = name;

Here m is the first letter of member.
Why write behavior first and then properties when defining a class.
In other words, why you don’t need to define variables when you define a class?

access permission

// arrayone.cpp -- small arrays of integers
#include <iostream>

using namespace std;

const double PI = 3.14;

//访问权限
//公共public 保护protected 私有private
//public    类内外均可访问
//protected 仅类内可以访问（子可访问父亲）
//private   仅类内可以访问（子不可访问父亲）
class Person 
{
    
    
    public:
        string name_;
    protected:
        string car_;
    private:
        int password_;
    public:
        void func()
        {
    
    
            name_ = "Libo";
            car_ = "benz";
            password_ = 123;
        }

};


int main()
{
    
    
    Person p1;
    p1.name_ = "Jerry";
    // p1.car_ = "new";
    // p1.password_ = 1234;

    p1.func();

    system("pause");
    return 0;
}

• Public authority public: accessible inside and outside the class
• Protected permissions: Only accessible within the class (child can access the father)
• Private authority private: Only accessible within the class (child cannot access the father)

The difference between struct and class

• struct default public permissions public
• class Default private permissions private