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NaN Field
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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

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: 4.6, 4.5, 4, 3.5, 3.0, 2.0, 1.1

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

XNA Framework

Supported in: 3.0, 2.0, 1.0

.NET for Windows Phone apps

Supported in: Windows Phone 8.1, Windows Phone Silverlight 8.1, Windows Phone Silverlight 8

Portable Class Library

Supported in: Portable Class Library
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