在不知道 c 中的密钥的情况下移位密码

Question

我正在编写一个程序来解决一个随机代码。（代码不会有大写字母，任何形式的符号，如句号）代码使用移位密码而不知道密钥，它也可以加密代码，但我会稍后再处理。现在我尝试先输出所有 25 个结果。

但是，如果我输入“背靠背”之类的内容，它会在最后输出一个问号。

这是我的代码

#include <stdio.h>
#include <string.h>
#include <stdlib.h>

int main() {
  char code[400];
  char after[400];  // variable initialization
  int i, x, choice, z, temp, y;
  printf("                     Welcome\n");
  printf("Enter your code here:\n");
  scanf("%[^'\n']s", code);
  printf("Press 1 to Decrypt\nPress 2 to encrypt\nPress 3 to Exit\n");
  scanf("%d", &choice);

  // case 1 is decryption
  switch (choice) {
    case 1:
      for (x = 1; x <= 25; x++) {
        for (i = 0; (i <= 400 && code[i] != 0); i++)  // for loop
        {
          if (code[i] == 32) {  // 32 means space in ascii code
            after[i] = 32;
            continue;  // if there is a space it will continue
          }
          if (code[i] + x > 122) {  // 122 is z in ascii code
            after[i] = code[i] + x;  // if it is higher than 'z'
            after[i] = (after[i] - 122) + 96;  // it start counting form 'a'
            continue;
          } else {
            after[i] = code[i] + x;
            // if nothing is wrong,it starting adding the key
          }
        }
        printf("After decrypting:%s\n", after);
        printf("%s\n", code);
      }
      break;

    // case 2 is ecnrypt so its not important
    case 2:
      x = 5;
      for (i = 0; (i <= 400 && code[i] != 0); i++)  // for loop
      {
        if (code[i] == ' ') {
          continue;
        }
        if (code[i] + x > 122) {
          code[i] = code[i] + x;
          code[i] = (code[i] - 122) + 96;
          continue;
        } else {
          code[i] = code[i] + x;
        }
      }
      printf("After decrypting:%s", code);
      break;

    // not important as well
    case 3:
      printf("GOODBYE");
      break;

    // not important as well
    default:
      printf("Errors");
      return 0;
  }
}

Answer 1

要解决移位密码，您只需要一本字典和密文的前十个单词左右。尝试所有可能性并根据您的字典测试每个“解码”的明文单词。选择匹配率最高的密码。

Answer 2

你忘了空终止after。

也许你应该这样做：

    for (i = 0; (i <= 400 && code[i] != 0); i++) {
      if (code[i] == 32) {
        after[i] = ...
      } else if (code[i] + x > 122) {
        after[i] = ...
      } else {
        after[i] = ...
      }
    }
    after[i] = '\0'; // <-- This line is missing.
    printf("After decrypting:%s\n", after);
    printf("%s\n", code);