using System;

public class Program

{

    public static void Main()

    {

    string chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";

    var stringChars = new char[5];

    var random = new Random();

​

for (int i = 0; i < stringChars.Length; i++)

{

    stringChars[i] = chars[random.Next(chars.Length)];

}

​

var finalString = new String(stringChars);

        Console.WriteLine(finalString);

    }

}

​

// abcdefghijklmnopqrstuvwxyz0123456789