C# WinApp การเช็คค่า string/double ครับ

 string Ans;
        void GetAns() {
            timer1.Stop();
          
            if (string.IsNullOrEmpty(lblEq.Text))
            {
                score++;
                MessageBox.Show("ได้คะแนนฟรี 1 คะแนน");
                lblStatus.Write($"ได้คะแนนฟรี 1 คะแนน");
                log.Debug($"ได้คะแนนฟรี 1 คะแนน");
            }
            else if (string.IsNullOrEmpty( txtAns.Text.Trim()))
            {
                MessageBox.Show($"คำตอบคือ \n{Ans}");
                score--;
                log.Debug($"Invalid input. Please enter a valid Ans.");
                
            }
            else
            {
                log.Debug($"GetAns:{txtAns.Text} and {Ans}");
                if (txtAns.Text.Trim() == Ans.Trim())
                {
                    score++;
                }
                else
                {
                    MessageBox.Show($"คำตอบคือ \n{Ans}");
                    score--;
                }

            }
    
            lblStatus.Write($"คำตอบคือ {Ans}");
           
            txtScore.Text = score.ToString();
            lblStatus.Write($"โจทย์ {count} ข้อ คุณทำได้ {score} คะแนน คิดเป็น {score / count * 100:0.000}%");
            GetProblems();

        }

private static QuestionItem GetProblemsPSUnit01() {
    List<Prefixe> Prefixs = new List<Prefixe>() {
    new Prefixe("เทระ", "tera-", "T-", "10^12", 1000000000000d),
    new Prefixe("จิกะ", "giga-", "G-", "10^9", 1000000000d),
    new Prefixe("เมกะ", "mega-", "M-", "10^6", 1000000d),
    new Prefixe("กิโล", "kilo-", "k-", "10^3", 1000d),
    new Prefixe("เฮกโต", "hecto-", "h-", "10^2", 100d),
    new Prefixe("เดคา", "deca-", "da-", "10^1", 10d),

    new Prefixe("เดซิ", "deci-", "d-", "10^-1", 0.1d),
    new Prefixe("เซนติ", "centi-", "c-", "10^-2", 0.01d),
    new Prefixe("มิลลิ", "milli-", "m-", "10^-3", 0.001d),
    new Prefixe("ไมโคร", "micro-", "μ-", "10^-6", 0.000001d),
    new Prefixe("นาโน", "nano-", "n-", "10^-9", 0.000000001d),
    new Prefixe("พิโค", "pico-", "p-", "10^-12", 0.000000000001d),
   };
    List<string> units = new List<string>() { "เมตร", "กรัม", "วินาที", "แอมแปร์", "เคลวิน", "โมล", "เฮิรตซ์", "นิวตัน", "จูล", "วัตต์", "โวลต์", "โอห์ม", "ฟารัด" };
    QuestionItem question = new QuestionItem();
    string a;
    Prefixe prefixe = Prefixs[RandomNumber.Randomnumber(0, Prefixs.Count)];
    string _uint = units[RandomNumber.Randomnumber(0, units.Count)];
    double anws = 0.00;
    double randomNum;
    if (prefixe.factor >= 10d)
    {
        randomNum = (r.NextDouble().ToDouble(r.Next(2, 5))) * (Math.Pow(10, r.Next(1, 5))) * prefixe.factor;
        a = randomNum.ToString("F0");

    }
    else
    {
        randomNum = r.NextDouble().ToDouble(r.Next(2, 5)) * (Math.Pow(10, r.Next(1, 5))) * prefixe.factor;
        a = randomNum.ToString("##0.############################################");

    }
    anws = randomNum / prefixe.factor;
    string s = $"{a} {_uint} มีค่าเป็นกี่ {prefixe.prefixeTh}{_uint}?";

    question = new QuestionItem(anws, s);



    return question;
}