ช่วยเขียนโค๊ด C# บวกจำนวนเหรียญจากเครื่องหยอดเหรียญหน่อยคับ คือว่าต้องการให้จำนวนเหรียญที่หยอดเข้ามานั้นบวกโชว์ไปเรื่อยๆๆอ่ะคับ

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.IO.Ports;

namespace testSerial
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
        string iData;
        //int a;
        private void Form1_Load(object sender, EventArgs e)
        {
            if (!serialPort1.IsOpen)
                serialPort1.Open();
        }
        private void Form1_close(object sender, EventArgs e)
        {
            if (serialPort1.IsOpen)
                serialPort1.Close();
        }
        public static byte[] ConvertStringToByteArray(string stringToConvert)
        {
            return (new UnicodeEncoding()).GetBytes(stringToConvert);
        }
        private void ReceiveData(object s, EventArgs e)
        {
            byte[] myBytes = ConvertStringToByteArray(iData);
            string hexString = BitConverter.ToString(myBytes);
            // Replace the - seperator for an whitespace
            hexString = hexString.Replace("-", " ");
            tbHex.Text = hexString; // Out put data that can be display in hex string.
            int x;
            if (tbHex.Text == "3F 00 06 00 12 00 01 00 03 00 3F 00")
                textBox1.Text = "1";
            else if (tbHex.Text == "3F 00 06 00 12 00 06 00 03 00 3F 00")
                textBox1.Text = "1";
            else if (tbHex.Text == "3F 00 06 00 12 00 05 00 03 00 3F 00")
                textBox1.Text = "2";
            else if (tbHex.Text == "3F 00 06 00 12 00 03 00 03 00 3F 00")
                textBox1.Text = "5";
            else if (tbHex.Text == "3F 00 06 00 12 00 04 00 03 00 3F 00")
                textBox1.Text = "10";
            x = Convert.ToInt32(textBox1.Text);


        }
        private void serRf_DataReceived(object sender, SerialDataReceivedEventArgs e)
        {
            iData = serialPort1.ReadExisting();
            this.Invoke(new EventHandler(ReceiveData));
        }
    }
}