Modulo doesn't work

Question

I know this will seem like a really stupid question, but I just don't get why this isn't working. This:

 System.out.println(5 % .10);

And it's returning:

0.09999999999999973

I really have NO IDEA. I'm just learning Java, and I'm pretty good with C#, so I tried with C# to. C# seemed to return the same thing also.

Answer 1

As others explained, this is due to inaccuracies caused by floating point precision.

You should use BigDecimal, in this case the remainder method for precise arithmetic involving decimals.

BigDecimal number = new BigDecimal(5);
BigDecimal divisor = new BigDecimal("0.1");
BigDecimal result = number.remainder(divisor);
System.out.println(result); // 0

Answer 2

This is due to floating-point precision. 0.10 cannot be represented exactly in binary. Therefore the result is not exactly 0.10 and is hence not modded down to 0.

This will work with 0.25 because 0.25 can be represented exactly in binary.

EDIT:

In general, any number that can be expressed as a fraction with a power-of-two in the denominator can be expressed exactly in IEEE floating-point. (provided it doesn't over/underflow)

Answer 3

You're doing floating point arithmetic. 0.1 has no exact representation as a float.