using System;

using System.Text;

using System.Text.RegularExpressions;

​

public class Program

{

    public static void Main()

    {

        var regex = new Regex(@"^[a-zA-Z0-9#@][a-zA-Z0-9#@\-\.]{1,149}$");

        var rand = new Random();

        var start = new string[]{"1", "a", "#", "@", };

        var andThen = new string[]{"1", "a", "#", "@", "-", "."};

        const int numTests = 10;

        const int testLength = 150;

        for (var i = 0; i < numTests; ++i)

        {

            var s = start[0];

            var builder = new StringBuilder(s);

            for (var j = 1; j < testLength; ++j)

            {

                var r = rand.Next() % andThen.Length;

                builder.Append(andThen[r]);

            }

​

            var test = builder.ToString();

            var isMatch = regex.IsMatch(test);

            Console.WriteLine($"{test} {isMatch}");

        }

    }

}