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

int prepare_key(char *key) {
    if (key == NULL || strlen(key) == 0) {
        return 0;
    }

    char alphabet[27] = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";   //加密比对码
    char modified_key[27];
    int index = 0;

    for (int i = 0; i < strlen(key); i++) { 
        char ch = toupper(key[i]);  //将读入的小写字母转换成大写
// 如果字符是大写字母且不在 modified_key 中，则添加到 modified_key 中
        if (ch >= 'A' && ch <= 'Z' && strchr(modified_key, ch) == NULL) {
            modified_key[index++] = ch;         
        }
    }
// 遍历字母表，将不在 modified_key 中的字母添加到 modified_key 中
    for (int i = 0; i < 26; i++) {
        if (strchr(modified_key, alphabet[i]) == NULL) {
            modified_key[index++] = alphabet[i];
        }
    }

    strcpy(key, modified_key);
    return 1;
}

int main() {
    char key[27];
    printf("请输入加密初始值：\n");
    scanf("%s", key);

    if (prepare_key(key)) {
        printf("Prepared key:\n%s", key);
    } else {
        printf("Error key.\a\a\a");
    }

    return 0;
}