用c++写一个栅栏密码的加密和解密

以下是一个 C++ 实现的栅栏密码加密和解密程序：

#include <iostream>
#include <string>

using namespace std;

string fence_cipher_encrypt(string plain_text, int rails) {
    string fence[rails];
    int rail = 0;
    int direction = 1;
    
    for (char c : plain_text) {
        fence[rail] += c;
        rail += direction;
        
        if (rail == 0 || rail == rails - 1) {
            direction = -direction;
        }
    }
    
    string cipher_text;
    for (string rail : fence) {
        cipher_text += rail;
    }
    
    return cipher_text;
}

string fence_cipher_decrypt(string cipher_text, int rails) {
    string fence[rails];
    int rail = 0;
    int direction = 1;
    
    for (char c : cipher_text) {
        fence[rail] += '-';
        rail += direction;
        
        if (rail == 0 || rail == rails - 1) {
            direction = -direction;
        }
    }
    
    int index = 0;
    for (int i = 0; i < rails; i++) {
        for (int j = 0; j < fence[i].length(); j++) {
            if (fence[i][j] == '-') {
                fence[i][j] = cipher_text[index];
                index++;
            }
        }
    }
    
    string plain_text;
    rail = 0;
    direction = 1;
    for (int i = 0; i < cipher_text.length(); i++) {
        plain_text += fence[rail][0];
        fence[rail] = fence[rail].substr(1);
        rail += direction;
        
        if (rail == 0 || rail == rails - 1) {
            direction = -direction;
        }
    }
    
    return plain_text;
}

int main() {
    string plain_text = "HELLO WORLD";
    int rails = 3;
    
    string cipher_text = fence_cipher_encrypt(plain_text, rails);
    cout << cipher_text << endl; // HOLELWRDLO
    
    string decrypted_text = fence_cipher_decrypt(cipher_text, rails);
    cout << decrypted_text << endl; // HELLO WORLD
    
    return 0;
}

使用方式示例：

string plain_text = "HELLO WORLD";
int rails = 3;

string cipher_text = fence_cipher_encrypt(plain_text, rails);
cout << cipher_text << endl; // HOLELWRDLO

string decrypted_text = fence_cipher_decrypt(cipher_text, rails);
cout << decrypted_text << endl; // HELLO WORLD

其中 `fence_cipher_encrypt` 函数接受两个参数：明文 `plain_text` 和栅栏数量 `rails`，返回加密后的密文。`fence_cipher_decrypt` 函数接受两个参数：密文 `cipher_text` 和栅栏数量 `rails`，返回解密后的明文。