.98 cents instead of .99

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joshdalrymple2000@yahoo.com - 29 Jan 2006 22:25 GMT

double totalCost = 3.91, amountPaid = 4.00;
int totalChange;

totalChange = (int)((amountPaid - totalCost) * 100);
System.out.println(totalChange);

it keeps saying the answer is 8... can any one help?

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Stefan Schulz - 30 Jan 2006 11:33 GMT

You have run into a bad case of rounding error. doubles are not exactly
the number you wish to represent, and thus, amountPaid - totalCost may
be a tiny bit less then 9, which gets rounded down to 8 by the int cast.

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Googmeister - 30 Jan 2006 13:42 GMT

> double totalCost = 3.91, amountPaid = 4.00;
> int totalChange;
[quoted text clipped - 3 lines]
>
> it keeps saying the answer is 8... can any one help?

Try (int) (Math.round(100 * (amountPaid - totalCost)))

Or better use, store the amount as an int/long in pennies
or use BigDecimal to avoid floating point precision issues.

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Roedy Green - 30 Jan 2006 14:40 GMT

>Try (int) (Math.round(100 * (amountPaid - totalCost)))
>
>Or better use, store the amount as an int/long in pennies
>or use BigDecimal to avoid floating point precision issues.

for more discussion of the problem of currency calculation see
http://mindprod.com/jgloss/currency.html

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Canadian Mind Products, Roedy Green.
http://mindprod.com Java custom programming, consulting and coaching.

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.98 cents instead of .99

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