Generating a random string in C# uses the same concepts that are used to generate a random number in C#. The `StringBuilder` class and the `NextDouble()` method in the `Random` class are used to generate a random string.

# Algorithm

- Use the `Random.NextDouble()` method to generate a float (`flt`) that is between $0.0$ and $1.0$ and is inclusive.
- Multiply `flt` with $25$ and take the `Floor` of the result. This will return an integer (`shift`) that is between $0$ and $25$ and is inclusive.
- Add the `shift` integer to $65$, which is the ASCII value of the character **A**. This will return an inclusive value between $65$ and $90$, which will be the ASCII value of some character. Converting that value to a character will return an uppercase character.
- Repeat the above steps​ as required to obtain a randomly generated string.

# Code

The code snippet below illustrates the algorithm described above:

using System.Text;
using System;
class GenerateRandomString
{
    static void Main()
    {
      int length = 7;
      
      // creating a StringBuilder object()
      StringBuilder str_build = new StringBuilder();  
      Random random = new Random();  

      char letter;  

      for (int i = 0; i < length; i++)
      {
        double flt = random.NextDouble();
        int shift = Convert.ToInt32(Math.Floor(25 * flt));
        letter = Convert.ToChar(shift + 65);
        str_build.Append(letter);  
      }  
      System.Console.WriteLine(str_build.ToString());
    }
}

How to generate a random string in C#

Use Random.NextDouble() and StringBuilder to generate a random string of uppercase characters in C#.