Double.NaN Field

 

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

Namespace:   System
Assembly:  mscorlib (in mscorlib.dll)

public const double NaN

Field Value

Type: System.Double

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.");

Universal Windows Platform
Available since 8
.NET Framework
Available since 1.1
Portable Class Library
Supported in: portable .NET platforms
Silverlight
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1
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