The following C# code prints 0.1 - why?
var s = "0.1";
var dbl = Double.Parse(s);
var dcml = Convert.ToDecimal(dbl);
Console.WriteLine(dcml.ToString());
Isn't 0.01 not representable in binary, therefore it should print 0.100000001490116 ?
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Andriy Volkov
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1https://stackoverflow.com/questions/1421520/formatting-doubles-for-output-in-c-sharp – Alex May 17 '19 at 16:28
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3Note that 0.100000001490116 is the result of calling `Single.Parse`, not `Double.Parse`. – Jon Skeet May 17 '19 at 16:29
1 Answers
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The value of dbl is precisely 0.1000000000000000055511151231257827021181583404541015625.
That's 0.1 to 17 significant digits.
The documentation for Convert.ToDecimal(Double) states:
The Decimal value returned by this method contains a maximum of 15 significant digits. If the value parameter contains more than 15 significant digits, it is rounded using rounding to nearest.
The conversion from Single (aka float) is documented to truncate earlier:
The Decimal value returned by this method contains a maximum of seven significant digits. If the value parameter contains more than seven significant digits, it is rounded using rounding to nearest.
If you call Convert.ToDecimal(Double) with a value initially converted from 0.1f, it will display 0.100000001490116:
double dbl = 0.1f;
decimal dcml = (decimal) dbl;
Console.WriteLine(dcml);
Jon Skeet
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alright, this does answer my question, but I'd still like to know what's going on with Single in the same case, as the Single's behavior casts doubt on our understanding of the Decimal's behavior. – Andriy Volkov May 17 '19 at 16:40
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@zvolkov: Doh - I shouldn't have used `var`. That was the problem. If you convert it with `double x = 0.1f;` then it's fine. – Jon Skeet May 17 '19 at 16:45
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