Stuff

import java.io.*;

public class Vigenere2 {
    public static void main(String args[]) {
        int k;
	int i;
	int p;

	String casos = null;
	String message = null;
	String key = null;
	String alpha = new String("ABCDEFGHIJKLMNOPQRSTUVWXYZ");

	BufferedReader buff = new BufferedReader(new InputStreamReader(System.in));
	try {	
	System.out.println("Bienvenido, porfavor, eliga una opción. Escriba 1 si desea encriptar su mensaje, 2 si desea desencriptar y 3 para salir: ");
	casos = buff.readLine(); k = Integer.parseInt(casos);

	switch (k)
	{
	case 1:
	    try {

			System.out.print("Mensaje: ");
			message = buff.readLine();
			message = message.toUpperCase();

			System.out.print("Llave: ");
			key = buff.readLine();
			key = key.toUpperCase();
		
			char[] output = new char[message.length()];
			for (i = 0; i < message.length(); i++) {

				if (alpha.indexOf(message.charAt(i)) >= 0) {
					p = (int)message.charAt(i) + (int)key.charAt(i%key.length());
					output[i] = alpha.charAt(p >= 0 ? p % alpha.length() : alpha.length() + p);
				} else {
					output[i] = message.charAt(i);
				}
			}

			System.out.print(new String(output)+"\n");

		} catch (IOException e) {

			System.out.print("Error.\n");
			System.exit(1);

		}
	
	
	break;

	case 2:
	    try {

			System.out.print("Mensaje: ");
			message = buff.readLine();
			message = message.toUpperCase();

			System.out.print("Llave: ");
			key = buff.readLine();
			key = key.toUpperCase();
		
			char[] output = new char[message.length()];
			for (i = 0; i < message.length(); i++) {

				if (alpha.indexOf(message.charAt(i)) >= 0) {
					p = (int)message.charAt(i) - (int)key.charAt(i%key.length());
					output[i] = alpha.charAt(p >= 0 ? p % alpha.length() : alpha.length() + p);
				} else {
					output[i] = message.charAt(i);
				}
			}

			System.out.print(new String(output)+"\n");

		} catch (IOException e) {

			System.out.print("Error.\n");
			System.exit(1);

		}
	
	break;

        case 3:
	    System.out.println("Hasta la vista!");
	    System.exit(0);
        break;

        default:
	    System.out.println("Error!");
	    System.exit(0);
        break;

	}
	} catch (IOException e) {

		System.out.print("Error.\n");
		System.exit(1);

	}
    }
}