IMPLEMENT CAESAR CIPHER WITH VARIABLE KEY

It is an encryption technique in which each plaintext letter is to be replaced with one a fixed number of

places (in following implementation, key) down the alphabet. This example is with a shift of three

(key=3), so that a B in the plaintext becomes E in the ciphertext.

#include <stdio.h>
#include <conio.h>
#include <string.h>
#include <ctype.h>
void main()
    {
    clrscr();
    char message[80],ciphertext[80],decryptedtext[80];
    int i;

    printf("Enter original message : ");
    scanf("%[^\n]",message);

    for(i=0; i<strlen(message); ++i)
        {
        if(isalpha(message[i]))
            {
            if((message[i]+3)>'z')ciphertext[i]='a'+message[i]+3-'z'-1;
            else ciphertext[i]=message[i]+3;
            }
        else
            {
            ciphertext[i]=message[i];
            }
        }
    ciphertext[i]='\0';
    printf("Cipher text            : %s\n",ciphertext);

    getch();
    }