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# Double.NaN Field

.NET Framework 4.5

Represents a value that is not a number (NaN). This field is constant.

Namespace:  System
Assembly:  mscorlib (in mscorlib.dll)
```public const double NaN
```

A method or operator returns NaN when the result of an operation is undefined. For example, the result of dividing zero by zero is NaN, as the following example shows. (But note that dividing a non-zero number by zero returns either PositiveInfinity or NegativeInfinity, depending on the sign of the divisor.)

```double zero = 0.0;
Console.WriteLine("{0} / {1} = {2}", zero, zero, zero/zero);
// The example displays the following output:
//         0 / 0 = NaN
```

In addition, a method call with a NaN value or an operation on a NaN value returns NaN, as the following example shows.

```double nan1 = Double.NaN;

Console.WriteLine("{0} + {1} = {2}", 3, nan1, 3 + nan1);
Console.WriteLine("Abs({0}) = {1}", nan1, Math.Abs(nan1));
// The example displays the following output:
//       3 + NaN = NaN
//       Abs(NaN) = NaN
```

Use the IsNaN method to determine whether a value is not a number. The Equality operator considers two NaN values to be unequal to one another. In general, Double operators cannot be used to compare Double.NaN with other Double values, although comparison methods (such as Equals and CompareTo) can. The following example illustrates the difference in behavior between Double comparison operators and methods.

```using System;

public class Example
{
public static void Main()
{
Console.WriteLine("NaN == NaN: {0}", Double.NaN == Double.NaN);
Console.WriteLine("NaN != NaN: {0}", Double.NaN != Double.NaN);
Console.WriteLine("NaN.Equals(NaN): {0}", Double.NaN.Equals(Double.NaN));
Console.WriteLine("! NaN.Equals(NaN): {0}", ! Double.NaN.Equals(Double.NaN));
Console.WriteLine("IsNaN: {0}", Double.IsNaN(Double.NaN));

Console.WriteLine("\nNaN > NaN: {0}", Double.NaN > Double.NaN);
Console.WriteLine("NaN >= NaN: {0}", Double.NaN >= Double.NaN);
Console.WriteLine("NaN < NaN: {0}", Double.NaN < Double.NaN);
Console.WriteLine("NaN < 100.0: {0}", Double.NaN < 100.0);
Console.WriteLine("NaN <= 100.0: {0}", Double.NaN <= 100.0);
Console.WriteLine("NaN >= 100.0: {0}", Double.NaN > 100.0);
Console.WriteLine("NaN.CompareTo(NaN): {0}", Double.NaN.CompareTo(Double.NaN));
Console.WriteLine("NaN.CompareTo(100.0): {0}", Double.NaN.CompareTo(100.0));
Console.WriteLine("(100.0).CompareTo(Double.NaN): {0}", (100.0).CompareTo(Double.NaN));
}
}
// The example displays the following output:
//       NaN == NaN: False
//       NaN != NaN: True
//       NaN.Equals(NaN): True
//       ! NaN.Equals(NaN): False
//       IsNaN: True
//
//       NaN > NaN: False
//       NaN >= NaN: False
//       NaN < NaN: False
//       NaN < 100.0: False
//       NaN <= 100.0: False
//       NaN >= 100.0: False
//       NaN.CompareTo(NaN): 0
//       NaN.CompareTo(100.0): -1
//       (100.0).CompareTo(Double.NaN): 1
```

The following example illustrates the use of NaN:

```      Double zero = 0;

// This condition will return false.
if ((0 / zero) == Double.NaN)
Console.WriteLine("0 / 0 can be tested with Double.NaN.");
else
Console.WriteLine("0 / 0 cannot be tested with Double.NaN; use Double.IsNan() instead.");
```

#### .NET Framework

Supported in: 4.5.1, 4.5, 4, 3.5, 3.0, 2.0, 1.1, 1.0

#### .NET Framework Client Profile

Supported in: 4, 3.5 SP1

#### Portable Class Library

Supported in: Portable Class Library

#### .NET for Windows Store apps

Supported in: Windows 8

Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.