Question

我想在C中制作Vigenere Cipher。https://www.youtube.com/watch?v=9zASwVoshiM这是关于Vigenere Cipher的信息。我的代码工作对某些情况不起作用，比如加密“世界，打招呼！” as“xoqmd，rby gflkp！”使用“baz”作为关键字而不是将其加密为xomd，szz fl。另一个例子是：使用“BaZ”作为关键字将“BaRFoo”加密为“CaQGon”，而是将其加密为CakGo。我的代码如下，请帮助我：

#include<stdio.h>
#include<cs50.h>
#include<ctype.h>  
#include<string.h>
#include<stdlib.h>

int main(int argc, string argv[]) {
    //string plaintext;

    string key;
    if (argc != 2) {
        printf("Please run the programme again this time using a command line argument!\n");
        return 1;
    }
    key = argv[1];
    int keys[strlen(key)];

    for (int m = 0; m< strlen(key); m++) {
        if (isalpha(key[m]) == false) {
            printf("Re-Run The programme without any symbols.\n");
            return 1;
        }
    }

    for (int b = 0; b < strlen(key); b++) {
        if (isupper(key[b]) == false) {
            keys[b] = key[b] - 'a';
        }
        else {
            keys[b] = key[b] - 'A';
        }
    }

    //printf("Enter a string which should be encrypted: \n");
    string plaintext = GetString();
    int plength = strlen(plaintext);
    int klength = strlen(key);
    string ciphertext = key;

    for (int u = 0; u<plength; u++) {

        if (isalpha(plaintext[u]) == false) {
            printf("%c", plaintext[u]);
            continue;
        }

        int value = u % klength;
        ciphertext[u] = (keys[value] + plaintext[u]);
        if ((islower(plaintext[u])) && (ciphertext[u])>'z') {
            ciphertext[u] = ciphertext[u] - 'z' + 'a' - 1;
        }

        if ((isupper(plaintext[u])) && (ciphertext[u])>'z') {
            ciphertext[u] = ciphertext[u] - 'Z' + 'A' - 1;
        }

        printf("%c", ciphertext[u]);
    }

    printf("\n");

    return 0;
}

Answer 1

NULL

string ciphertext = key;应该以空白开头，不应设置为密钥。

ciphertext

这是不正确的，因为ciphertext[u] = ciphertext[u] - 'z' + 'a' - 1;可能超出范围。性格应该在＆＃39; a＆＃39;之间。到了＆＃39;。使用mod ciphertext[u]运算符确保字符在范围内。例如：

Answer 2

许多小问题（ciphertext需要动态分配，并以plaintext的副本开始，而不是key;需要对字母表的长度进行mod计算;不正确计算;将错误打印到stderr）以及可以进行的大量小优化（组合循环;组合if子句;将key长度保存到变量之前）。您的代码的返工：

#include <stdio.h>
#include <cs50.h>
#include <ctype.h>
#include <string.h>
#include <stdlib.h>

int main(int argc, string argv[]) {

    if (argc != 2) {
        fprintf(stderr, "Please run the program again with a command line argument!\n");
        return 1;
    }

    string key = argv[1];
    int key_length = strlen(key);
    int keys[key_length];

    for (int i = 0; i < key_length; i++) {
        if (!isalpha(key[i])) {
            fprintf(stderr, "Re-run The program without any symbols.\n");
            return 1;
        }

        keys[i] = toupper(key[i]) - 'A';
    }

//  printf("Enter a string which should be encrypted: \n");

    string plaintext = GetString();
    int text_length = strlen(plaintext);
    string ciphertext = strcpy(malloc(text_length + 1), plaintext);

    for (int i = 0, j = 0; i < text_length; i++) {
        if (!isalpha(plaintext[i])) {
            continue;
        }

        int index = j++ % key_length;

        ciphertext[i] = (toupper(plaintext[i]) - 'A' + keys[index]) % (1 + 'Z' - 'A');

        ciphertext[i] += isupper(plaintext[i]) ? 'A' : 'a';
    }

    printf("%s\n", ciphertext);

    free(ciphertext);

    return 0;
}

加密“世界，打招呼！” as“xoqmd，rby gflkp！”用键“baz”

使用键“BaZ”将“BaRFoo”加密为“CaQGon”

Vigenere Cipher

2 个答案: