请扮演一个资深程序员，编写 基于C语言的Vigenere 密码加解密，在指定的目录下建立明文文件，输入任意选取的密钥， 加密后得到密文（包含大写字母和小写字母）文件。在已知密钥的情况下将密文（包含大写字母和小写字母）文件解密得到明文（包含大写字母和小写字母）文件

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

#define MAX_SIZE 1024

void encrypt(char* plaintext, char* key, char* ciphertext);
void decrypt(char* ciphertext, char* key, char* plaintext);

int main() {
char plaintext[MAX_SIZE];
char ciphertext[MAX_SIZE];
char key[MAX_SIZE];
char filename[MAX_SIZE];
FILE *fp;
int choice;

printf("请选择操作：\n1.加密\n2.解密\n");
scanf("%d", &choice);

printf("请输入明文文件名：");
scanf("%s", filename);

fp = fopen(filename, "r");
if (fp == NULL) {
printf("打开文件失败！\n");
exit(1);
}

fgets(plaintext, MAX_SIZE, fp);
fclose(fp);

printf("请输入密钥：");
scanf("%s", key);

switch (choice) {
case 1:
encrypt(plaintext, key, ciphertext);
printf("加密后的密文为：\n%s\n", ciphertext);

printf("请输入密文文件名：");
scanf("%s", filename);

fp = fopen(filename, "w");
if (fp == NULL) {
printf("打开文件失败！\n");
exit(1);
}
fputs(ciphertext, fp);
fclose(fp);
break;

case 2:
decrypt(plaintext, key, ciphertext);
printf("解密后的明文为：\n%s\n", plaintext);

printf("请输入明文文件名：");
scanf("%s", filename);

fp = fopen(filename, "w");
if (fp == NULL) {
printf("打开文件失败！\n");
exit(1);
}
fputs(plaintext, fp);
fclose(fp);
break;

default:
printf("无效操作！\n");
break;
}

return 0;
}

void encrypt(char* plaintext, char* key, char* ciphertext) {
int len_p = strlen(plaintext);
int len_k = strlen(key);

for (int i = 0; i < len_p; i++) {
if (plaintext[i] >= 'a' && plaintext[i] <= 'z') {
ciphertext[i] = (plaintext[i] - 'a' + key[i % len_k] - 'a') % 26 + 'a';
}
else if (plaintext[i] >= 'A' && plaintext[i] <= 'Z') {
ciphertext[i] = (plaintext[i] - 'A' + key[i % len_k] - 'a') % 26 + 'A';
}
else {
ciphertext[i] = plaintext[i];
}
}
ciphertext[len_p] = '\0';
}

void decrypt(char* ciphertext, char* key, char* plaintext) {
int len_c = strlen(ciphertext);
int len_k = strlen(key);

for (int i = 0; i < len_c; i++) {
if (ciphertext[i] >= 'a' && ciphertext[i] <= 'z') {
plaintext[i] = (ciphertext[i] - 'a' - key[i % len_k] + 'a' + 26) % 26 + 'a';
}
else if (ciphertext[i] >= 'A' && ciphertext[i] <= 'Z') {
plaintext[i] = (ciphertext[i] - 'A' - key[i % len_k] + 'a' + 26) % 26 + 'A';
}
else {
plaintext[i] = ciphertext[i];
}
}
plaintext[len_c] = '\0';
}