While Loops

Introduction

The while loop is a special form of loop that will continue to repeat as long as the test condition evaluates to true.

Syntax

In java, the while loop takes the form of

while(test condition)
{
   ...
   statements
   ...
}

In this particular situation, the while loop will continue to iterate as long as the test condition evaluates to true

Uses

A while loop is useful in any situation where you don't know beforehand how often you want to repeat the block of code. Consider the following situation instance:

import javax.swing.JOptionPane;

public class Input
{
  public static void main(String args[]) 
  {
    String done;
    done = JOptionPane.showInputDialog("Enter a phrase, type quit to finish");
    
    while(!done.equals("quit"))
    {
         System.out.println("Hello " + name);
         done = JOptionPane.showInputDialog("Enter a phrase, type quit to finish");
    }
  }
}

This code will repeatedly ask the user for input, and display that input, until the user types quit.

Assignments

Ignore the //<--Comment--> comments until you've read the assignment modification at the bottom

Asst. 1 Guess my number program

import javax.swing.JOptionPane;

public class GuessNumber
{
  public static void main(String args[]) 
  {
    int myNumber = 29;
    String number;
    int guess;
    //<--Min and max variables go here-->

    //get guess from user
    number = JOptionPane.showInputDialog("Pick a number between 1 and 100"); //<--Show user min and max-->

    //convert number from string to integer
    guess = Integer.parseInt(number);
    while(guess != myNumber) {
      if(guess < myNumber)
      {
        //<--Modify min or max variables here-->
	number = JOptionPane.showInputDialog("Too low, please try again); //<--Show user min and max-->
      }
      else
      {
        //<--Modify min or max variables here-->
      	number = JOptionPane.showInputDialog("Too high, please try again); //<--Show user min and max-->
      }

      //convert number from string to integer
      guess = Integer.parseInt(number);
    }
    JOptionPane.showMessageDialog(null, "Congratulations, you picked the right number");
  }
}

This program will ask the user to guess the number until the user guesses correctly. How can this program be improved?

Modify this program so that the program tells the user whether they guessed too high or too low. Hints have been placed in the program in comments.

Answer

Asst. 2 Pick up stones

Note: May want to read up on Logical Operators before doing this one.

import javax.swing.JOptionPane;

public class Stones
{
  public static void main(String args[]) 
  {
    int totalStones = 21;

    String number;
    int removed;

    //<--Uncomment when doing assignment-->
    //JOptionPane.showMessageDialog(null, "Pick up 1-3 stones until all are gone");

    //get guess from user
    number = JOptionPane.showInputDialog("There are " + totalStones + " stones, pick up how many?");

    //convert number from string to integer
    removed= Integer.parseInt(number);

    //<--Ask the user for another input while removed > 3 or removed <= 0 or removed > totalStones-->
    
    //remove stones from pile
    totalStones -= removed;

    while(totalStones > 0) {
      number = JOptionPane.showInputDialog("There are " + totalStones + " stones, pick up how many?");

      //convert number from string to integer
      removed= Integer.parseInt(number);

      //<--Ask the user for another input while removed > 3 or removed <= 0 or removed > totalStones-->
    
      //remove stones from pile
      totalStones -= removed;
    }
    JOptionPane.showMessageDialog(null, "All the stones are gone");
  }
}

This program allows the user to remove stones, as many as they want, until there are no stones remaining.

Modify this program so that the user cannot remove more than 3 stones at a time, and so that the user cannot remove more stones than there are available.

Answer

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