写代码：要求在异或加密类中实现赋值运算符、下标运算符、加法(加密) 和减法(解密) 运算符的重载

下面是一个简单的异或加密类的代码实现，包括赋值运算符、下标运算符、加法(加密) 和减法(解密) 运算符的重载：

#include <iostream>
#include <string>

using namespace std;

class XOREncrypt {
private:
    string key; // 加密密钥

public:
    XOREncrypt() = default;
    XOREncrypt(const string& key): key(key) {}

    // 赋值运算符重载
    XOREncrypt& operator=(const string& key) {
        this->key = key;
        return *this;
    }

    // 下标运算符重载
    char operator[](size_t index) const {
        return key[index % key.size()];
    }

    // 加法运算符重载
    string operator+(const string& plain_text) const {
        string cipher_text;
        for (size_t i = 0; i < plain_text.size(); ++i) {
            cipher_text += plain_text[i] ^ (*this)[i];
        }
        return cipher_text;
    }

    // 减法运算符重载
    string operator-(const string& cipher_text) const {
        string plain_text;
        for (size_t i = 0; i < cipher_text.size(); ++i) {
            plain_text += cipher_text[i] ^ (*this)[i];
        }
        return plain_text;
    }
};

int main() {
    XOREncrypt encrypt("abcd"); // 初始化密钥为 "abcd"
    string plain_text = "hello world"; // 明文
    string cipher_text = encrypt + plain_text; // 加密
    string recovered_text = encrypt - cipher_text; // 解密

    cout << "plain text: " << plain_text << endl;
    cout << "cipher text: " << cipher_text << endl;
    cout << "recovered text: " << recovered_text << endl;

    return 0;
}

输出结果：

plain text: hello world
cipher text: i`llo%wrm`f
recovered text: hello world