How to generate a string randomly using C#?

Generating random strings in C# is useful for creating passwords, test data, or unique identifiers. There are several approaches to generate random strings, from simple character-based methods to more advanced techniques using predefined character sets.

Syntax

Following is the basic syntax for generating random strings using Random class −

Random random = new Random();
char randomChar = (char)random.Next(startValue, endValue);

Following is the syntax using a character array −

char[] chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZ".ToCharArray();
char randomChar = chars[random.Next(chars.Length)];

Using ASCII Values for Random String Generation

This method generates random characters by converting ASCII values to characters. ASCII values 65-90 represent uppercase letters A-Z −

using System;
using System.Text;

class Program {
   static void Main() {
      StringBuilder str = new StringBuilder();
      char c;
      Random random = new Random();
      
      for (int i = 0; i < 6; i++) {
         c = Convert.ToChar(Convert.ToInt32(Math.Floor(26 * random.NextDouble() + 65)));
         str.Append(c);
      }
      
      Console.WriteLine("Random string: " + str.ToString());
   }
}

The output of the above code is −

Random string: QMKFBT

Using Character Array for Mixed Case Strings

This approach uses a predefined character set for more control over the allowed characters −

using System;
using System.Text;

class Program {
   static void Main() {
      string chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";
      StringBuilder result = new StringBuilder();
      Random random = new Random();
      
      for (int i = 0; i < 8; i++) {
         result.Append(chars[random.Next(chars.Length)]);
      }
      
      Console.WriteLine("Random alphanumeric string: " + result.ToString());
   }
}

The output of the above code is −

Random alphanumeric string: K3mN9pQr

Using GUID for Unique Random Strings

For truly unique strings, you can use Guid.NewGuid() which generates a globally unique identifier −

using System;

class Program {
   static void Main() {
      string randomGuid = Guid.NewGuid().ToString();
      Console.WriteLine("GUID string: " + randomGuid);
      
      string shortGuid = Guid.NewGuid().ToString("N").Substring(0, 8);
      Console.WriteLine("Short GUID: " + shortGuid);
   }
}

The output of the above code is −

GUID string: 6f8ac3e4-9b2d-4f5a-8c1e-7d3b9a8e4f2c
Short GUID: a7b3c4d5

Comparison of Methods

Conclusion

C# provides multiple ways to generate random strings: ASCII-based methods for simple character ranges, character arrays for custom sets, and GUIDs for guaranteed uniqueness. Choose the method based on your specific requirements for character variety and string length.