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package ciphers;

import java.util.Scanner;

/**

* A Java implementation of Caesar Cipher. /It is a type of substitution cipher in which each letter

* in the plaintext is replaced by a letter some fixed number of positions down the alphabet. /

*

* @author FAHRI YARDIMCI

* @author khalil2535

*/

public class Caesar {

/**

* Encrypt text by shifting every Latin char by add number shift for ASCII Example : A + 1 -> B

*

* @param message

* @param shift

* @return Encrypted message

*/

public static String encode(String message, int shift) {

String encoded = "";

shift %= 26;

final int length = message.length();

for (int i = 0; i < length; i++) {

// int current = message.charAt(i); //using char to shift characters because ascii

// is in-order latin alphabet

char current = message.charAt(i); // Java law : char + int = char

if (IsCapitalLatinLetter(current)) {

current += shift;

encoded += (char) (current > 'Z' ? current - 26 : current); // 26 = number of latin letters

} else if (IsSmallLatinLetter(current)) {

current += shift;

encoded += (char) (current > 'z' ? current - 26 : current); // 26 = number of latin letters

} else {

encoded += current;

}

}

return encoded;

}

/**

* Decrypt message by shifting back every Latin char to previous the ASCII Example : B - 1 -> A

*

* @param encryptedMessage

* @param shift

* @return message

*/

public static String decode(String encryptedMessage, int shift) {

String decoded = "";

shift %= 26;

final int length = encryptedMessage.length();

for (int i = 0; i < length; i++) {

char current = encryptedMessage.charAt(i);

if (IsCapitalLatinLetter(current)) {

current -= shift;

decoded += (char) (current < 'A' ? current + 26 : current); // 26 = number of latin letters

} else if (IsSmallLatinLetter(current)) {

current -= shift;

decoded += (char) (current < 'a' ? current + 26 : current); // 26 = number of latin letters

} else {

decoded += current;

}

}

return decoded;

}

/**

* @param c

* @return true if character is capital Latin letter or false for others

*/

private static boolean IsCapitalLatinLetter(char c) {

return c >= 'A' && c <= 'Z';

}

/**

* @param c

* @return true if character is small Latin letter or false for others

*/

private static boolean IsSmallLatinLetter(char c) {

return c >= 'a' && c <= 'z';

}

public static void main(String[] args) {

Scanner input = new Scanner(System.in);

System.out.println("Please enter the message (Latin Alphabet)");

String message = input.nextLine();

System.out.println(message);

System.out.println("Please enter the shift number");

int shift = input.nextInt() % 26;

System.out.println("(E)ncode or (D)ecode ?");

char choice = input.next().charAt(0);

switch (choice) {

case 'E':

case 'e':

System.out.println(

"ENCODED MESSAGE IS \n" + encode(message, shift)); // send our function to handle

break;

case 'D':

case 'd':

System.out.println("DECODED MESSAGE IS \n" + decode(message, shift));

default:

System.out.println("default case");

}

input.close();

}

}