`//
// Created by 송기훈 on 2023/03/13.
//

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



#pragma warning(disable: 4326 4996 6031)

int main(void)
{
    char sMsg[80];
    int nKey = 3, nMore = true;
    while (nMore) {
        printf("? ");
        gets(sMsg);
        switch (sMsg[0]) {
            case 0:
                nMore = false;
                break;
            case '@':
                printf("  Key ? ");
                gets(sMsg);
                nKey = atoi(sMsg);
                break;
            default:
                printf("  ");
                char Encrypt(char ch, int nKey);
                for (int i = 0; sMsg[i]; i++)
                    putchar(Encrypt(sMsg[i], nKey));
                putchar('\n');
        }
        putchar('\n');
    }
    printf("Bye, ....\n\n");
}

char Encrypt(char chr, int nKey)
{
    if (isalpha(chr)) {
        //char cBgn = (chr & 0x60) + 1;
        char cBgn = (isupper(chr)) ? 'A' : 'a';
        chr = (chr - cBgn + nKey + 26) % 26 + cBgn;
    }
    return chr;
}

/*****

? I Love You

  L Oryh Brx



? @

Key ? -3



? L Oryh Brx

  I Love You



?

Bye, ....

****/`