Article
11/18/2011

Char.IsNumber Method (String, Int32)

Microsoft Silverlight will reach end of support after October 2021. Learn more.

Indicates whether the character at the specified position in a specified string is categorized as a number.

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

Syntax

'Declaration
Public Shared Function IsNumber ( _
    s As String, _
    index As Integer _
) As Boolean

public static bool IsNumber(
    string s,
    int index
)

Parameters

s
Type: System.String
A string.

index
Type: System.Int32
The character position in s.

Return Value

Type: System.Boolean
true if the character at position index in s is a number; otherwise, false.

Exceptions

Exception	Condition
ArgumentNullException	s is nulla null reference (Nothing in Visual Basic).
ArgumentOutOfRangeException	index is less than zero or greater than the last position in s.

Remarks

This method determines if a Char is of any numeric Unicode category. In addition to digits, numbers include characters, fractions, subscripts, superscripts, Roman numerals, currency numerators, and encircled numbers. This method contrasts with the IsDigit method, which determines if a Char is a radix-10 digit.

Character positions in a string are indexed starting from zero.

Valid numbers are members of the UnicodeCategory.DecimalDigitNumber, UnicodeCategory.LetterNumber, or UnicodeCategory.OtherNumber category.

If the Char object at position index is the first character of a valid surrogate pair, the IsNumber method determines whether the surrogate pair forms a numeric digit. For example, the Aegean numbering system consists of code points U+10107 through U+10133. The following example uses the ConvertFromUtf32 method to instantiate a string that represents AEGEAN NUMBER ONE. As the output from the example shows, the IsNumber method returns true if it is passed the high surrogate of AEGEAN NUMBER ONE. However, if it is passed the low surrogate, it considers only the category of the low surrogate and returns false.

Dim surrogate As String = ChrW(&hD800) + ChrW(&hDD07)     ' AEGEAN NUMBER ONE
For ctr As Integer = 0 To surrogate.Length - 1
   outputBlock.Text += String.Format("U+{0:X4} at position {1}: {2}",  
                     Convert.ToUInt16(surrogate(ctr)), ctr,  
                     Char.IsNumber(surrogate, ctr)) + vbCrLf
Next
' The example displays the following output:
'       U+D800 at position 0: True
'       U+DD07 at position 1: False

string surrogate = "\uD800\uDD07";         // AEGEAN NUMBER ONE
for (int ctr = 0; ctr < surrogate.Length; ctr++)
   outputBlock.Text += String.Format("U+{0:X4} at position {1}: {2}",
                     Convert.ToUInt16(surrogate[ctr]), ctr,
                     Char.IsNumber(surrogate, ctr)) + "\n";
// The example displays the following output:
//       U+D800 at position 0: True
//       U+DD07 at position 1: False

Examples

The following example demonstrates IsNumber.


Module Example

   Public Sub Demo(ByVal outputBlock As System.Windows.Controls.TextBlock)

      Dim str As String
      str = "non-numeric"

      outputBlock.Text &= Char.IsNumber("8"c) & vbCrLf      ' Output: "True"
      outputBlock.Text += String.Format(Char.IsNumber(str, 3)) & vbCrLf    ' Output: "False"

   End Sub

End Module

using System;

public class Example
{
   public static void Demo(System.Windows.Controls.TextBlock outputBlock)
   {
      string str = "non-numeric";

      outputBlock.Text += Char.IsNumber('8').ToString() + "\n";     
      outputBlock.Text += Char.IsNumber(str, 3).ToString() + "\n";
   }
}
// This example produces the following output:
//       True  
//       False

Version Information

Silverlight

Supported in: 5, 4, 3

Silverlight for Windows Phone

Supported in: Windows Phone OS 7.1, Windows Phone OS 7.0

XNA Framework

Supported in: Xbox 360, Windows Phone OS 7.0

Platforms

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.

Change History

Date	History	Reason
	Added information about how the method handles surrogate pairs.	Information enhancement.

Partager via