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a little bug

Posted on 2008-06-17
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Last Modified: 2010-03-30
hi,
 I have  a small problem in java, but not in c or c++. I guess the type problem . However, I don't know how to fix. please help.

if the input is 10.19 & 10.31, the result is supposed to be 12. However, I have Pennies are 12.000084.

if i change the line pennies = (amountReceived - amountDue) *100;
to pennies = amountReceived*100 - amountDue *100;

I will get correct answer because values are converted to int before do calculation. I just wonder what if I do some division program. How cold I avoid this problem? Thanks

import java.util.*;
import java.io.*;
class Demo
{
	public static void main ( String[] args)
	{
		Scanner temp;
		float amountDue, amountReceived;
 
		System.out.print("Enter the amountDue : " );
		temp = new Scanner( System.in);
        amountDue      = temp.nextFloat();
 
		System.out.print("Enter the amountReceived :");
		temp = new Scanner( System.in);
		amountReceived = temp.nextFloat();
 
		float pennies, nickels, dimes, quarters, dollars;
		float container;
 
		pennies = (amountReceived - amountDue) *100;
		System.out.print("Pennies are " + pennies + "\n");
 
	}
}

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Question by:valleytech
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5 Comments
 
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Assisted Solution

by:spoxox
spoxox earned 300 total points
ID: 21809212
Floating point numbers' representation at the machine's level are not exact, so errors like this happen.

A Formatter or System.out.format can help.

See http://java.sun.com/j2se/1.5.0/docs/api/java/util/Formatter.html
0
 
LVL 11

Accepted Solution

by:
spoxox earned 300 total points
ID: 21809217

                System.out.format("Pennies are %4.2f", pennies);
0
 
LVL 6

Assisted Solution

by:psychic_zero
psychic_zero earned 200 total points
ID: 21809261
Maybe this is due to you're using float type. Maybe you can use number formatting to make sure the result is 12 by adding this code:

pennies = (amountReceived - amountDue) *100;
 
NumberFormat formatter = new DecimalFormat("##"); 
String s = formatter.format(pennies);
 
System.out.print("Pennies are " + pennies + "\n");

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Expert Comment

by:psychic_zero
ID: 21809265
To do my way, I think you need to include import java.text.*;
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Author Comment

by:valleytech
ID: 21809403
and pennies must be s


for future reference

import java.text.*;

pennies = (amountReceived - amountDue) *100;
 
NumberFormat formatter = new DecimalFormat("##");
String s = formatter.format(pennies);
 
System.out.print("Pennies are " + pennies + "\n");
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