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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
 
LVL 11

Assisted Solution

by:spoxox
spoxox earned 300 total points
Comment Utility
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
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Accepted Solution

by:
spoxox earned 300 total points
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                System.out.format("Pennies are %4.2f", pennies);
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LVL 6

Assisted Solution

by:psychic_zero
psychic_zero earned 200 total points
Comment Utility
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
Comment Utility
To do my way, I think you need to include import java.text.*;
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Author Comment

by:valleytech
Comment Utility
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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