Question

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Floating point inaccuracy examples

When using the modulo operator in java I’m not getting the number I expect to get.

Heres what I’m doing:

double input = 5.59;
System.out.println("Output: " + (input % 2));

I expect to see 1.59 as the result however it is printing out 1.5899999999999999. Any clue as to why this may be?

Answer 1

This comes from floating point inaccuracy, here is a great SO answer explaining exactly what is happening.

If you want it to round out the number you need to use formatting like this:

double input = 5.59;
System.out.format("Output: %.2f%n", (input % 2));

• The “%” tells the formatter to replace itself with the first numeric argument. You can add as many of these as you want.
• The “.2” tells the formatter to format the number with two places after the decimal.
• The “f” just tells the formatter it is a floating point number.
• The “%n” is a new line character appropriate to the platform running the application. You should always use “%n”, rather than “\n”.

Here is some good documentation for all this.

Hope this helps!