Char.IsNumber Method (String, Int32)


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

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

public static bool IsNumber(
	string s,
	int index


Type: System.String

A string.

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.

Exception Condition

s is null.


index is less than zero or greater than the last position in s.

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.


The IsNumber(String, Int32) method is not intended to determine whether a string consists of numeric characters (for example, by calling the method for each character in a string). To determine whether a string consists of numeric characters, call one of the overloads of the TryParse method (such as Int32.TryParse or Double.TryParse of an integral or floating point type.

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(String, Int32) 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(String, Int32) 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.

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

The following example demonstrates IsNumber.

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"

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