The core of creating a class in C is to use the class keyword to define the structure and encapsulate data and operations. The specific steps are as follows: 1. Use the class keyword to define the class, pay attention to ending with a semicolon; 2. Create an object and access members through a dot. The objects on the heap need to use pointers and -> operators and manually release memory; 3. Use constructors to automatically initialize members, and multiple constructors can be overloaded; 4. Control access rights through private, protected, and public, which is default to private, and public members are visible to the outside world. Master these basic syntax and key points to quickly get started with the use of the class.

It is actually not difficult to create a class in C. The core is to use class keyword to define a structure and encapsulate data and operations together. As long as you master the basic grammar and a few key points, you can get started quickly.

1. Basic syntax: Use class to define classes

The first step in creating a class is to use the class keyword, followed by the class name, then a pair of curly braces {} , and finally end with a semicolon ; (this is easy to forget).

 class Person {
public:
    std::string name;
    int age;

    void introduce() {
        std::cout << "Hi, I&#39;m " << name << " and I&#39;m " << age << " years old." << std::endl;
    }
};

• public: means that the next member is public and can be accessed externally.
• name and age are data members of the class.
• introduce() is a member function of the class that performs an operation.

Tip: Remember to add a semicolon after class definition, which is a common mistake for many novices.

2. Create an object and access a member

Classes are just templates, and when they are actually used, you need to create "instances", that is, objects.

 Person p1;
p1.name = "Alice";
p1.age = 30;
p1.introduce(); // Output: Hi, I'm Alice and I'm 30 years old.

• Object p1 uses the Person class structure.
• Access the properties and methods of the object through dots .

If you want to create objects on the heap, you can do this:

 Person* p2 = new Person();
p2->name = "Bob";
p2->age = 25;
p2->introduce();
delete p2; // Don't forget to release the memory

• When using pointers, use -> to access members.
• Remember to manually allocate memory, otherwise memory leaks.

3. Constructor makes initialization more convenient

Is it troublesome to manually set name and age every time? Initialization can be automatically completed with a constructor.

 class Person {
public:
    std::string name;
    int age;

    // Constructor Person(std::string n, int a) {
        name = n;
        age = a;
    }

    void introduce() {
        std::cout << "Hi, I&#39;m " << name << " and I&#39;m " << age << " years old." << std::endl;
    }
};

How to use:

 Person p3("Charlie", 28);
p3.introduce();

• The constructor name is the same as the class name, and there is no return value.
• Multiple constructors can be overloaded to accommodate different situations.

4. Control access rights: private, protected and public

By default, the members of class are private and cannot be accessed directly from the outside. If you want some members to be visible to the outside world, add public: .

 class Person {
private:
    std::string name;
    int age;

public:
    Person(std::string n, int a) {
        name = n;
        age = a;
    }

    void introduce() {
        std::cout << "Hi, I&#39;m " << name << " and I&#39;m " << age << " years old." << std::endl;
    }
};

At this time, you cannot write p.name = "Tom" directly, but you can operate it through member functions.

• private : Only accessible inside the class.
• protected : Similar to private, but allows subclass access (for inheritance).
• public : Anyone can access it.

Basically that's it. There are many advanced usages of C classes, such as destructors, operator overloading, friend functions, etc., but it is enough to master these four parts when you first get started.

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