Getting wrong answers for conversion

[Alisha Burke]

Hi all,


I've been working on a program for base conversion.
After making some adjustments I am yet to get the "correct" answer for my conversion. For example when i key in 100 i get 10 as my answer.

I am using a label to set the text of my answer but all it does is take the number entered in the textfield i guess. Appreciate all replies.

I understand that my Compute method doesn't get called. How do i accomplish that?

import java.awt.*;
import java.applet.*;
import java.awt.event.*;
import java.io.*;
 
/*
 This is an applet that enables the user to enter the number and the base 
 system of number entered. Upon clicking the Convert button, the program should 
 display the number, the positional weightage of each digit of the number, and
 the decimal equivalent of the number
*/
 
public class Testing1 extends Applet implements ActionListener {
//declare all components
Label numbersystemLabel;  //Top Label
Label numberLabel;  //Middle Label next to the number TextField
Label baseLabel;  //Middle Label next to the base TextField
Label answerLabel; //Bottom Label for the answer

static String numberkeyin;  //number that is entered in the textfield
        static String bintype="binary";  //convert binary base to decimal
static String octtype="octal";  //convert octal base to decimal
static String yrtype="";

static String real= "";

TextField numberField;
TextField baseField;

Button convert;

int Answer;

Panel p1;
Panel p2;
Panel p3;
    
    public void init() {
    
    p1 = new Panel ();
    p2 = new Panel ();
    p3 = new Panel ();
    
    p1.setLayout(new BorderLayout(25,25));
    p2.setLayout(new GridLayout(2,2,2,2));
    p3.setLayout(new BorderLayout(25,25));
    
    numbersystemLabel=new Label ("Number System");
p1.add("North",numbersystemLabel);
    
    numberLabel=new Label ("Enter the number : ");
 p2.add(numberLabel);
 numberField=new TextField(9);
 p2.add(numberField);
 
 baseLabel=new Label ("Enter the base system  ");
 p2.add(baseLabel);
 baseField=new TextField(9);
 p2.add(baseField);
 
 convert=new Button ("Convert");
 convert.addActionListener(this);
 
 answerLabel=new Label ("Decimal Equivalent : ");
p1.add("South",answerLabel);

p3.add("North",p2);
p3.add("South",convert);

p1.add("Center",p3);
add(p3);
add(p1);

}


  public void actionPerformed(ActionEvent event) {
                                                                                                                     
Answer=Integer.parseInt(numberField.getText());
 
yrtype=baseField.getText();

answerLabel.setText(real);


if (yrtype.equals(bintype)){
       real="Decimal Equivalent: " +Answer  ;
       }
    else {
       real="Decimal Equivalent: Daddy's girl ";
       }
            
repaint();
}
 
   private void Compute()  {

int i;
int countlength;
char bit;
 
    Answer = 0; // initialize the answer to zero.
    countlength = numberkeyin.length();    
        // find the length of the binary number string.
 
        for( i=1; i<=countlength; i++) {
bit = numberkeyin.charAt(countlength-i);
 // extract each binary digit, starting from the right.
if( bit == '1' ) {
Answer += Math.pow(2.0,i-1.0);

   // The digit was a "1", so add it's decimal equivalent to the answer.
}

}
}
    public void paint(Graphics g)  {
//power 
String a= "2" ; String v= "4";
String b= "2" ; String w= "3";
String c= "2" ; String x= "2";
        String d= "2" ; String y= "1";
        String e= "2" ; String z= "0";
  
  g.setFont(new Font ("Helvetica",Font.ITALIC+Font.BOLD,20));
  g.drawString("" +e +"     " +d +"     " +c +"     " +b +"     " +a, 350, 250 );
  g.setFont(new Font ("Helvetica",Font.ITALIC+Font.BOLD,12));
  g.drawString(" " +v +"           " +w +"            " +x +"            " +y +"            " +z, 355, 235 );
 
    }
 }
  
 

[ February 09, 2005: Message edited by: Alisha Burke ]

[Liam Tiarnach]

Hi Alisha...

Okay I took a look at it and made these changes to your compute method...

  private void Compute()  {
  Answer = 0; // initialize the answer to zero.
char [] bits = numberkeyin.toCharArray(); // convert numberkeyin string to a char array
  int powers = 0; // initialize the power exponent value to 0
  for( int i=bits.length-1; i >= 0 ; i--) { 
/* int i is initialized to the length to the char array size -1 since arrays are 0 indexed
and .length is 1 indexed... i.e a 4 element array has a length of 4 by is indexed 0 to 3 
and as you have noted that binary reads from right to left so we need to start off with
the right most which would be the last element not the first */
if( bits[i] == '1' ) { // checkes if element in char array is 1 and then does the math
Answer += Math.pow(2.0,powers);// uses powers since it increments to do the conversion
   // The digit was a "1", so add it's decimal equivalent to the answer.
}powers++; // increments powers regardless of whether the digit is 1 or 0
}
}

included are comment documenting the changes... basically we know that binary number are read right
to left, so we must start at the last element and work our way to the first. So as an example 1011 is
converted to a 4 element char array {'1','0','1','1'} with the index increasing from left to right.
And this is where a problem arises... If we use the array index to compute what power 2 is raised to
the first element ( left most ) will be 0 with the last in our example being 3. So whether we count up
or down the coversion will be wrong. So what we have to do is either reverse the array
( which would require even more code ) or simple reverse how we increase the power that 2 is raised by.
i.e.
3-2-1-0 array index reading from right to left
1-1-0-1 element values reversed ( actual is 1011 = 11)
1-2-3-4 exponent values reading from right to left

the reason this was done in reverse is so that it follows how we would logically interpet a binary number...

Also what was done was that the String numberkeyin that get returned from you numberField.getText() method
is converted to a char array using the method java.lang.String.toCharArray() which all Strings are able to
utilize. Doing the binary conversion is much easier with a char array than using the charAt() method...
at least I think so...

Next... you mentioned that your Compute method does not get called...
So here is another snippet that I modified to show you how to call it from your action performed method...

  public void actionPerformed(ActionEvent event) {
    numberkeyin=numberField.getText(); // gets the number input
    yrtype=baseField.getText(); // gets the type of conversion input
    Compute();// call to your compute method, which is called before you update the answer label
  if (yrtype.equals(bintype)){
       real="Decimal Equivalent: " +Answer  ;// now answer will have a value once compute is done
       }
    else {
       real="Decimal Equivalent: Daddy's girl ";
       }
    answerLabel.setText(real);
}

here basically what was done was the call to Compute() was inserted before you updated your label.
A class can call it's own method just by calling it method name and parameters if any...

Simple example...

public void sayHello(){
   System.out.println("Hello);//outputs "Hello"
}
public int doSomeMath(int num1,int num2){
/* returns an int and takes two ints as arguements\parameters */
   return num1 + num2; this is where the int get returned...
}
public void callMethods(){ // yet another method
   sayHello();// calls sayHello which displays "Hello"
   int answer = doSomeMath(10,5);//calls do someMath which adds 10 and 5
   // and the returned value is assigned to answer...
}

Anyway here is you entire class so that you can get a better idea of what was done...

import java.awt.*;
import java.applet.*;
import java.awt.event.*;
import java.io.*;
/*
 This is an applet that enables the user to enter the number and the base 
 system of number entered. Upon clicking the Convert button, the program should 
 display the number, the positional weightage of each digit of the number, and
 the decimal equivalent of the number
*/
public class Testing1 extends Applet implements ActionListener {
//declare all components
Label numbersystemLabel;  //Top Label
Label numberLabel;  //Middle Label next to the number TextField
Label baseLabel;  //Middle Label next to the base TextField
Label answerLabel; //Bottom Label for the answer
static String numberkeyin;  //number that is entered in the textfield
  static String bintype="binary";  //convert binary base to decimal
static String octtype="octal";  //convert octal base to decimal
static String yrtype="";
static String real= "";
TextField numberField;
TextField baseField;
Button convert;
int Answer;
Panel p1;
Panel p2;
Panel p3;
 
public void init() {
 
  p1 = new Panel ();
  p2 = new Panel ();
  p3 = new Panel ();
  p1.setLayout(new BorderLayout(25,25));
  p2.setLayout(new GridLayout(2,2,2,2));
  p3.setLayout(new BorderLayout(25,25));
  numbersystemLabel=new Label ("Number System");
p1.add("North",numbersystemLabel);
  numberLabel=new Label ("Enter the number : ");
p2.add(numberLabel);
numberField=new TextField(9);
p2.add(numberField);
baseLabel=new Label ("Enter the base system  ");
p2.add(baseLabel);
baseField=new TextField(9);
p2.add(baseField);
convert=new Button ("Convert");
convert.addActionListener(this);
answerLabel=new Label ("Decimal Equivalent : ");
p1.add("South",answerLabel);
p3.add("North",p2);
p3.add("South",convert);
p1.add("Center",p3);
add(p3);
add(p1);
}
 
public void actionPerformed(ActionEvent event) {
  numberkeyin=numberField.getText(); // gets the number input
  yrtype=baseField.getText(); // gets the type of conversion input
  Compute();// call to your compute method, which is called before you update the answer label
if (yrtype.equals(bintype)){
    real="Decimal Equivalent: " +Answer  ;// now answer will have a value once compute is done
  }else{
  real="Decimal Equivalent: Daddy's girl ";
  }
  answerLabel.setText(real);
}
 
private void Compute()  {
  Answer = 0; // initialize the answer to zero.
char [] bits = numberkeyin.toCharArray(); // convert numberkeyin string to a char array
  int powers = 0; // initialize the power exponent value to 0
  for( int i=bits.length-1; i >= 0 ; i--) {
/* int i is initialized to the length to the char array size -1 since arrays are 0 indexed
and .length is 1 indexed... i.e a 4 element array has a length of 4 by is indexed 0 to 3
and as you have noted that binary reads from right to left so we need to start off with
the right most which would be the last element not the first */
if( bits[i] == '1' ) { // checkes if element in char array is 1 and then does the math
Answer += Math.pow(2.0,powers);// uses counter since it increments to do the conversion
   // The digit was a "1", so add it's decimal equivalent to the answer.
}
powers++; // increments counter regardless of whether the digit is 1 or 0
}
}
 
public void paint(Graphics g)  {
//power
String a= "2" ; String v= "4";
String b= "2" ; String w= "3";
String c= "2" ; String x= "2";
  String d= "2" ; String y= "1";
  String e= "2" ; String z= "0";
g.setFont(new Font ("Helvetica",Font.ITALIC+Font.BOLD,20));
g.drawString("" +e +"     " +d +"     " +c +"     " +b +"     " +a, 350, 250 );
g.setFont(new Font ("Helvetica",Font.ITALIC+Font.BOLD,12));
g.drawString(" " +v +"           " +w +"            " +x +"            " +y +"            " +z, 355, 235 );
 
}
/* This below was added by me so that I can quickly test the applet as a standalone application
basically I created a AWt Frame and stuck that Applet inside */
public static void main(String[] a) { // all standalone application require this "main" method signature
Testing1 t1 = new Testing1();// instantiated the Testing1 class and assigned to t1
Frame f = new Frame();// instantiated a Frame to put the Applet in
/* added a Window Listener, so that I can close the application down when I click the close button */
f.addWindowListener(new WindowAdapter(){public void windowClosing(WindowEvent we){ // an anonymous class
                                         we.getWindow().setVisible(false); // hides the window
 we.getWindow().dispose(); // releases the resources used by the window
 System.exit(0);}}); // exit the application
f.add(t1); // here I add Testing1 which is a Applet class ( extends Applet ) to the Frame (Window)
f.setSize(800,500); // sets the starting size of the window
t1.init();// call the applets init() method
f.setVisible(true);// display the window...
}
}

Hope this helps...

- Liam...

- ' He who never sleeps... '

[Alisha Burke]

Hi Liam,

Thanks a lot! I was so worried i'd never get the answer for my binary to decimal conversion. Now I can start working on my octal base conversion. Just wondering is it necessary to create another for loop for my octal to decimal conversion.

And there is one part of the code that you gave me that i just can't quite grasp after a couple of times reading it. I would really appreciate it if you could explain it in the simplest manner as possible.

for( int i=bits.length-1; i >= 0 ; i--)

I am confused:

a) with the bits.length is that the length() method your using there?
b} how come its i-- and not i++

I understand that binary reads from right to left and we need to start off with the right most element. I just don't understand how the code above manage to accomplish that.

[Liam Tiarnach]

Hi again ...

Okay, no problem... let's start off with the first question...

for( int i=bits.length-1; i >= 0 ; i--)

here we see the loop setup to run in reverse. So let break it down... ( you all ready know the for loop syntax, so I explain the code within...

int i = bits.length - 1

we initilize int i to be bits.length which using a 4 element array as an example would return a length of 4, but arrays are 0 indexed, so the last element in that array would be 3, so we subtract 1 to correct it.

i >= 0

basically, once we reach 0, end the loop

i--

each iteration decrements i by 1... a count down until it reaches 0 which ends the loop...

int powers = 0;

then we setup the loop so that is start with the right most element.

for( int index = bits.length - 1; index >= 0 ; index--) {

here i called "i" index for clarity...
next we check if the element is 1, if so then we add it binary value to our answer variable

if( bits[index] == '1' ) { // checkes if element in char array is 1 and then does the math
answer += Math.pow(2.0,powers);// uses powers since it increments to do the conversion
}

so now we are almost at the end of the loop, before we go to the next element to the left, we need to increase our exponent value by 1

powers++; // increments powers regardless of whether the digit is 1 or 0
}//end for loop... 

and the loop will count down until 0 is reached...
So using the example again using a 4 element array...
1-0-1-0 <- our char array representing a binary number 1010
0-1-2-3 <- our char array index values for each element in the char array
3-2-1-0 <- the exponent that we raise 2 by ( Math.pow(2.0,powers))

let step through it...
on the loops first run our index (index)starts at 3 (index = bits.length-1)
and our exponent (powers) is 0
at index 3, our binary number (bits[index]) is '0' so no math is done
answer current is 0
now that the check is done we increment our exponent (powers) by one (powers++)

on then second run of our loop, our index (index) is now 2 (index--)
and our exponent (powers) is now 1
at index 2, our binary number (bits[index]) is now '1' so we do the math (answer += Math.pow(2.0,powers)
answer is now 2
and all that done we increment our exponent (powers) by one again (powers++)

on the third run of out loop, you guessed it... index (index) is now 1 (index--)
our exponent (powers) is now 2
and at index 1, our binary number (bits[index]) is again '0' so no math
answer is still 2
and again we increment our exponent (powers) by one (powers++)

on the four and final run of our loop, index (index) is now 0 (index--)
our exponent (powers) has now reached 3
at index 0, our binary number (bits[index]) in '1' so we do the math (Math.pow(2.0,powers)
and answer is now 10 ( 2 + 8 )
although we still increment our exponent (powers) we no longer need it since our loop has ended...

Hopefully this helps...
[ February 09, 2005: Message edited by: Liam Tiarnach ]

[Layne Lund]

Often you use a for loop to count up from zero, but it doesn't have to. As described above, a for loop can just as easily count down. In this case, "i--" makes a lot of sense.

Layne

[Alisha Burke]

Thanks for the thourough explanation Liam... it sure cleared up a lot of my doubts.

*Smile with appreciation*

[Liam Tiarnach]

You might want to take a look at this method...

public void answerDisplayBuilder(Graphics g){  // this builds the display