Why double comparison not working with if condition?

Question

please see my below code and double comparison not working properly, though i have cast, double.Equal() method used, but no result. giving false

double b;
b = (1.6 + 1.6 + 1.6) / 3.0;

if( b == 1.6d)
{
     Console.WriteLine("True");
}
else
{
     Console.WriteLine("False");
}

// if( b.Equal(1.6))  -- No Result

This is a common problem with double comparisons This is a good answer: http://stackoverflow.com/questions/17333/what-is-the-most-effective-way-for-float-and-double-comparison — Display name, Apr 28 '17 at 19:11
An option would be to change your `double` to `decimal` if you're open too that solution. — I.B, Apr 28 '17 at 19:13

Andrii Litvinov · Accepted Answer · 2017-04-28T19:21:44.717

3

Because actual result value of operation (1.6 + 1.6 + 1.6) / 3.0 is 1.6000000000000003.

You need to use like:

if(Math.Abs(1.6d - value) < TOLERANCE)
{
     Console.WriteLine("True");
}
else
{
     Console.WriteLine("False");
}

And define acceptable tolerance.

Have a look at 0.30000000000000004.com

edited Apr 28 '17 at 19:21

answered Apr 28 '17 at 19:11

Andrii Litvinov

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Any reason for downvotes? – Andrii Litvinov Apr 28 '17 at 19:13
This explains why the if statement fails, but misses the more interesting question of why the operation is mathematically inaccurate. – BJ Myers Apr 28 '17 at 19:15
@BJMyers, the question was why condition fails. And I was about to provide a link to explanation. – Andrii Litvinov Apr 28 '17 at 19:19

Why double comparison not working with if condition?

1 Answers1