Code bug help for a beginner!!

Question

Ok, I've written this code so far. Everything was fine until I got to the IF condition. When I try compiling it it tells me that the 'a' variable in the IF condition expression may not have been initialised, which I don't really understand as it's been declared at the start of the program and even used fine beforehand in the switch statements.
Any ideas?
Thanks for any help. Here's the code.
import javax.swing.JOptionPane;
public class LetterProgram {
public static void main (String args[]) {
   String pickALet;
   String output;
   char letter;
   int guess;
   int a;
   pickALet = JOptionPane.showInputDialog ("please enter a lower case letter from (a to e)");
   output = "you selected a letter " + pickALet;
   letter = pickALet.charAt(0);
   switch (letter) {
   case 'a':
   a = 1;
   output = "you entered an a";
   break;
   case 'b':
   a = 2;
   output = "you entered a b";
   break;
   case 'c':
   a = 3;
   output = "you entered a c";
   break;
   case 'd':
   a = 4;
   output = "you entered a d";
   break;
   case 'e':
   a = 5;
   output = "you entered an e";
   break;
   default:
   output = "i did not recognise your entry";
   break;
   JOptionPane.showMessageDialog(null, output, "your letter", JOptionPane.INFORMATION_MESSAGE);
   guess =(int)(Math.random()*5 +1 ) ;
   System.out.println(guess);
   if (guess==a)
      System.out.println("The computer guessed the correct letter");
   else
      System.out.println("The computer guessed the letter incorrectly");
   System.exit(0);

Answer 1

It's better to add a default label to the switch; otherwise for most cases you will be setting the value twice, and it makes the intent of 'none of the above' clearer.
Pete