Q:

Allow the user to continue entering numbers until they choose to quit

This program's objective is to calculate the n-th Fibonacci number.  How do I allow the user to continue entering numbers until they choose to quit?  Thanks.  
public class FibonacciNUmbers
 {

 public static int calcFibNum(int x)
 {
  if (x == 0)
    return 0;
  else if (x == 1)
    return 1;
  else
    return calcFibNum(x-1) + calcFibNum(x-2);
 }

 public static void main(String[] args)
 {
  Scanner in = new Scanner(System.in);
  System.out.println("What number would you like to find the Fibonacci number for?"); 
  int x = in.nextInt();
  System.out.println("The Fibonacci number of " + x + " is " + calcFibNum(x));

  System.out.println("Would you like to find the Fibonaci number of another number?"); 
  String answer = in.next();
  if (answer.equalsIgnoreCase("Y"));
  {
      System.out.println("What number would you like to find the Fibonacci number for?"); 
      x = in.nextInt();
      System.out.println("The Fibonacci number for " + x + " is " + calcFibNum(x));
  }

  else 
  {
    System.out.println();
  }

}

}

A:

//start your while loop here
while (true)
{
    System.out.println("Would you like to find the Fibonacci number of another number?"); 
    String answer = in.next();
    if (answer.equalsIgnoreCase("Y"));
    {
        System.out.println("What number would you like to find the Fibonacci number for?"); 
        x = in.nextInt();
        System.out.println("The Fibonacci number for " + x + " is " + calcFibNum(x));
    }
    else 
    {
      System.out.println("Thanks for playing");
      break; // ends the while loop. 
    }
}

For loops are used when you can count things or have a set of things.   While loops are used when you're not sure how long it might go on for, or if you want it to continue until some event occurs (user pressing a certain letter for example)
Slight variation of the above that is probly a bit more elegant:
String answer = "Y";
//start your while loop here
while (answer.equals("Y")) {
    System.out.println("Would you like to find the Fibonacci number of another number?"); 
    answer = in.next(); //declare your variable answer outside the loop so you  can use it in the evaluation of how many times to do the loop. 
    if (answer.equalsIgnoreCase("Y"));
    {
        System.out.println("What number would you like to find the Fibonacci number for?"); 
        x = in.nextInt();
        System.out.println("The Fibonacci number for " + x + " is " + calcFibNum(x));
    }
    else 
    {
        System.out.println("Thanks for playing");
        // no need to break out. 
    }
}

