完成my_string 类运算符重载：

+=运算符：operator+=

下标运算符：operator[]

加法运算符：operator+

关系运算符：> 、 <、==

#include 
#include 
using namespace std;class my_string
{private:char *str; // 字符型指针（指向字符串首地址）int len; // 字符串长度public://无参构造my_string(){len = 15; // 给定15字节（可自己设置）str = new char[len]; // 堆区申请连续空间，存放字符串cout<<"无参构造"<str+i) = *(other.str+i);}cout<<"拷贝构造"<len = other.len;this->str = new char[len];for(int i=0; ilen+1; i++){*(this->str+i) = *(other.str+i);}cout<<"赋值拷贝构造"<len + 1]; // 申请空间存放原字符串strcpy(temp, this->str); //this->len += R.len; // += 长度更新delete this->str; // 释放原 str的空间this->str = new char[this->len+1]; //重新申请空间sprintf(this->str,"%s%s", temp, R.str); //重新赋值return *this;}// [] 运算符重载char &operator[](const int pos)const{return this->str[pos];}// + 算术运算符重载const my_string operator+(const my_string &R)const{my_string temp;temp.len = this->len+R.len;temp.str = new char[temp.len + 1];sprintf(temp.str,"%s%s", this->str, R.str);return temp;}// < 关系运算符重载bool operator<(const my_string &R)const{if(strcmp(this->str, R.str) < 0){return 1;}else{return 0;}}void show(){cout<<"str = "<