this pointer:
There is an implicit pointer variable this in the formal parameter list of each member function of the class. The type of the pointer variable is the type of the class to which the member function belongs
When the member function of the class is called in the program, the this pointer variable is automatically initialized to the address of the object issuing the function call
Use of this:
1. Distinguish between members and non-members
2. A method of a class needs to return a reference to the current object

	QS& set(int n, string name) {
		this->n = n;
		this->name = name;
		return *this;
	}

A simple analysis of the second method:

#include <iostream>
#include<string>
using namespace std;
class QS {
private://If omittedprivateMeansprivateAttributes 
	int n;
	string name;
public:
	QS() {
		this->n = 1;
		name = "wang";
		cout << "Constructor" << endl;
	}
	QS& set(int n, string name) {
		this->n = n;
		this->name = name;
		return *this;
	}
	~QS(){
		cout << "Destructor" << endl;
	}
	QS yyj(QS j)
	{
		j.n = this->n + 1;
		j.name = j.name + "+yyj";
		return j;
	}
	void show() {
		//printf("number=%d name=%s\n", this->n, this->name.c_str()); Use c_str() to change the string type name into a character array
		cout << "number= " << this->n << "   name= " << this->name << endl;
	}
};
int main()
{
	QS s;
	s.show();
	QS&ppt=s.set(100,"xiaobai");//There is no class that defines the name of ppt, but ppt points to s, which realizes data sharing and co-editing
	ppt.show();
	s.show();
	QS s1;
	s1.show();
	s1 = s.yyj(s1);//Here is that the temporary variable is not constructed but has a destructor
	s1.show();
	return 0;
}

Here, this->n=n assigns the integer variable n defined by this function to the private member n of this object
this->name=name is the name of the string type defined by this function is assigned to the private member name of this object

The results are as follows:
by

It can be seen that the defined QS& set function does not construct a new class, but directly points ppt to s, which realizes data sharing and co-editing
The first two destructors are temporary objects generated when the yyj function is called, and these objects will not call the constructor and can be assigned to realize the call of the copy constructor