// Author: Alexander K

// Comment: Generates random characters from a predefined character set.

​

using System;

using System.Text;

public class Program

{

    public class CharacterGenerator

    {

        private const string DefaultCharacterSet = "-_0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";

        private readonly Random _random;

        private readonly string _characterSet;

        public CharacterGenerator(string characterSet = DefaultCharacterSet)

        {

            _characterSet = characterSet;

            _random = new Random((int)DateTime.UtcNow.Ticks);

        }

        public string Generate(int size = 50)

        {

            var sb = new StringBuilder();

            var charSetSize = _characterSet.Length;

            for(var n = size; n > 0; n--)

            {

                var i = _random.Next(0, size) % charSetSize;

                sb.Append(_characterSet[i]);

            }

            return sb.ToString();

        }

    }

    public static void Main()

    {

        var generator = new CharacterGenerator();

        Console.WriteLine(generator.Generate());

        Console.WriteLine(generator.Generate(20));

        Console.WriteLine(generator.Generate(100));

    }

}

​