ExperimentStap.cs

using System;
using System.Text;
namespace ExperimentStap
{
    class Program
    {
        static readonly string chars = "ABCDEFGHIJKLMNOPQRSTUVWXYG";
        
        static void Main(string[] args)
        {
            Experiment();
            Console.ReadLine();
        }

        static void Experiment()
        {
            int count = 0;
            while(true)
            {
                count++;
                var str = GetRandomString(4);
                Console.Write(str+"細胞 ");
                if (str == "STAP")
                {
                    Console.WriteLine("{0}回目で陽性かくにん! よかった☆", count);
                    break;
                }
            }
        }

        static string GetRandomString(int length)
        {
            var sb = new StringBuilder(length);
            for (int i = 0; i < length; i++)
                sb.Append(chars[GetRandomNumber()]);
            return sb.ToString();
        }

        static int GetRandomNumber()
        {
            var bs = new byte[4];
            var rng = new System.Security.Cryptography.RNGCryptoServiceProvider();
            rng.GetBytes(bs);
            var num = System.BitConverter.ToInt32(bs, 0);
            return Math.Abs(num % chars.Length);
        }
    }
}