Char.IsLetterOrDigit() Method in C#

The Char.IsLetterOrDigit() method in C# determines whether a specified Unicode character is categorized as a letter or a decimal digit. This method is useful for validating input characters, parsing strings, and filtering alphanumeric content.

Syntax

Following is the syntax for the Char.IsLetterOrDigit() method −

public static bool IsLetterOrDigit(char ch);

There is also an overloaded version that works with strings −

public static bool IsLetterOrDigit(string s, int index);

Parameters

• ch − The Unicode character to evaluate.

• s − A string.

• index − The position of the character to evaluate in the string.

Return Value

Returns true if the character is a letter or digit; otherwise, false.

Using IsLetterOrDigit() with Individual Characters

Example with Digit Character

using System;

public class Demo {
   public static void Main() {
      bool res;
      char val = '1';
      Console.WriteLine("Value = " + val);
      res = Char.IsLetterOrDigit(val);
      Console.WriteLine("Is the value a letter or digit? = " + res);
   }
}

The output of the above code is −

Value = 1
Is the value a letter or digit? = True

Example with Special Character

using System;

public class Demo {
   public static void Main() {
      bool res;
      char val = '$';
      Console.WriteLine("Value = " + val);
      res = Char.IsLetterOrDigit(val);
      Console.WriteLine("Is the value a letter or digit? = " + res);
   }
}

The output of the above code is −

Value = $
Is the value a letter or digit? = False

Using IsLetterOrDigit() with Multiple Characters

Example with Mixed Character Types

using System;

public class Demo {
   public static void Main() {
      char[] chars = {'A', '5', '@', 'z', '0', ' ', 'X'};
      
      Console.WriteLine("Character\tIsLetterOrDigit");
      Console.WriteLine("-------------------------");
      
      foreach (char ch in chars) {
         bool result = Char.IsLetterOrDigit(ch);
         Console.WriteLine($"{ch}\t\t{result}");
      }
   }
}

The output of the above code is −

Character	IsLetterOrDigit
-------------------------
A		True
5		True
@		False
z		True
0		True
 		False
X		True

Using IsLetterOrDigit() with String Index

Example with String Validation

using System;

public class Demo {
   public static void Main() {
      string text = "Hello123!";
      
      Console.WriteLine($"Analyzing string: '{text}'");
      Console.WriteLine("Index\tChar\tIsLetterOrDigit");
      Console.WriteLine("-----------------------------");
      
      for (int i = 0; i < text.Length; i++) {
         bool result = Char.IsLetterOrDigit(text, i);
         Console.WriteLine($"{i}\t{text[i]}\t{result}");
      }
   }
}

The output of the above code is −

Analyzing string: 'Hello123!'
Index	Char	IsLetterOrDigit
-----------------------------
0	H	True
1	e	True
2	l	True
3	l	True
4	o	True
5	1	True
6	2	True
7	3	True
8	!	False

Common Use Cases

• Input Validation − Checking if user input contains only alphanumeric characters.

• String Parsing − Filtering out non-alphanumeric characters from text.

• Data Cleaning − Removing special characters while preserving letters and digits.

• Username Validation − Ensuring usernames contain only valid characters.

Conclusion

The Char.IsLetterOrDigit() method provides an efficient way to check if a character is either a letter or a digit. It supports both individual character checking and string-based character validation, making it versatile for input validation and text processing scenarios.