Char.IsNumber Method (String, Int32) (System)

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.NET Framework Class Library

Char.IsNumber Method (String, Int32)

Updated: December 2010

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

Visual Basic

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

public static bool IsNumber(
	string s,
	int index
)

Visual C++

public:
static bool IsNumber(
	String^ s, 
	int index
)

static member IsNumber : 
        s:string * 
        index:int -> bool

Parameters

s: Type: System.String
A string.

index: Type: System.Int32
The position of the character to evaluate 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 null.
ArgumentOutOfRangeException	index is less than zero or greater than the last position in s.

Remarks

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

Visual Basic


Dim utf32 As Integer = &h10107      ' AEGEAN NUMBER ONE
Dim surrogate As String = Char.ConvertFromUtf32(utf32)
For ctr As Integer = 0 To surrogate.Length - 1
   Console.WriteLine("U+{0:X4} at position {1}: {2}", 
                     Convert.ToUInt16(surrogate(ctr)), ctr,  
                     Char.IsNumber(surrogate, ctr))
Next
' The example displays the following output:
'       U+D800 at position 0: True
'       U+DD07 at position 1: False


int utf32 = 0x10107;      // AEGEAN NUMBER ONE
string surrogate = Char.ConvertFromUtf32(utf32);
for (int ctr = 0; ctr < surrogate.Length; ctr++)
   Console.WriteLine("U+{0:X4} at position {1}: {2}", 
                     Convert.ToUInt16(surrogate[ctr]), ctr,  
                     Char.IsNumber(surrogate, ctr));
// The example displays the following output:
//       U+D800 at position 0: True
//       U+DD07 at position 1: False

Examples

The following example demonstrates IsNumber.

Visual Basic


Module IsNumberSample
    Sub Main()
        Dim str As String
        str = "non-numeric"

        Console.WriteLine(Char.IsNumber("8"c))      ' Output: "True"
        Console.WriteLine(Char.IsNumber(str, 3))    ' Output: "False"
    End Sub
End Module


using System;

public class IsNumberSample {
	public static void Main() {
		string str = "non-numeric";

		Console.WriteLine(Char.IsNumber('8'));		// Output: "True"
		Console.WriteLine(Char.IsNumber(str, 3));	// Output: "False"
	}
}

Visual C++


using namespace System;
int main()
{
   String^ str =  "non-numeric";
   Console::WriteLine( Char::IsNumber( '8' ) ); // Output: "True"
   Console::WriteLine( Char::IsNumber( str, 3 ) ); // Output: "False"
}

Version Information

.NET Framework

Supported in: 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

Platforms

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

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

Reference

Char Structure

IsNumber Overload

System Namespace

Boolean

String

IsDigit

Change History

Date	History	Reason
December 2010	Added information about how the method handles surrogate pairs.	Information enhancement.

Date

History

Reason

December 2010

Added information about how the method handles surrogate pairs.

Information enhancement.