//

// 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, ....

****/`