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

#define CR 0x0d     //carriage return
#define ESC 0x1b    //Escape key
#define TAB 0x09
#define LF 0x0a     //Line feed
#define BACKSPACE 0x08
#define NULL 0      //Empty character
#define TRUE 1
#define FALSE 0
#define LENGTH 128   //size of the string

void rot13(char *string);
void input(char *string, int length);

void main()
{
    char phrase[LENGTH];
    char scrambled[LENGTH];

    puts("Type a phrase to be scrambled:");
    input(phrase,LENGTH);

/* copy the phrase before scrambling */

    strcpy(scrambled,phrase);

    rot13(scrambled);      //rot13 the phrase

    printf("The scrambled phrase is:\n");
    puts(scrambled);
}

void rot13(char *string)
{
    int count = 0;
    char c = '!';       //initialize c

    while(c)
    {
        c = string[count];
        if(isalpha(c))
        {
            if(toupper(c)>='A' && toupper(c)<='M')
                c+=13;
            else
                c-=13;
        }
        string[count] = c;
        count++;
    }
}

void input(char *string, int length)
{
    int done = FALSE;
    int index = 0;
    char ch;

    string[0] = NULL;   // init the buffer

    do
    {
        ch = getch();

/* Check to see if the buffer is full */

        if (index == length)
        {
            switch(ch)
            {
                case CR:
                    break;
                default:
                    ch = NULL;
                    break;
            }
        }

/* process the keyboard input */

        switch(ch)
        {
            case CR:        //Enter key
                putchar(ch);
                putchar(LF);
                string[index] = NULL;
                done = TRUE;
                break;
            case BACKSPACE:
                if(index==0)
                {
                    break;
                }
                else
                {
                    putchar(ch);
                    putchar(' ');
                    putchar(ch);
                    index--;
                    break;
                }
            case NULL:
                break;
            default:        //display & sto
                putchar(ch);
                string[index] = ch;
                index++;
                break;
        }
    }
    while(!done);
}