帮我看看这段代码,急

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using System.Text.RegularExpressions;namespace currency
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }        private void Form1_Load(object sender, EventArgs e)
        {
            this.textBox2.ReadOnly = true;
            this.button2.Enabled = false;
            this.TopMost = true;
           
            
        }
        private void radioButton1_CheckedChanged(object sender, EventArgs e)
        {
            if (radioButton1.Checked)
            {
                this.button2.Enabled = true;
                this.label2.Text = "美元";
            }
        }        private void radioButton2_CheckedChanged(object sender, EventArgs e)
        {
            if (radioButton2.Checked)
            {
                this.button2.Enabled = true;
                this.label2.Text = "英镑";
            }        }        private void radioButton3_CheckedChanged(object sender, EventArgs e)
        {
            if (radioButton3.Checked)
            {
                this.button2.Enabled = true;
                this.label2.Text = "日元";
            }
        }        private void button1_Click(object sender, EventArgs e)
        {
            if (this.textBox1.Text.Length == 0)
            {
                MessageBox.Show("wrong");
            }
            else
            {
                string str = this.textBox1.Text;
                string r = @"[1-9]\d+";
                str = System.Text.RegularExpressions.Regex.Match(str, r).ToString();  //RegularExpressions to match the number
                if (radioButton1.Checked)
                {
                    double num = (double.Parse(str)) / 8.0;
                    string str1 = num.ToString();
                    this.textBox2.Text = str1;
                }
                if (radioButton2.Checked)
                {
                    double num = (double.Parse(str)) / 10.0;
                    string str1 = num.ToString();
                    this.textBox2.Text = str1;
                }
                if (radioButton3.Checked)
                {
                    double num = (double.Parse(str)) * 10.0;
                    string str1 = num.ToString();
                    this.textBox2.Text = str1;
                }            }
        }        private void button2_Click(object sender, EventArgs e)
        {
            this.textBox1.Text = "";
            this.textBox2.Text = "";
            this.label2.Text = "美元";
        }        private void button3_Click(object sender, EventArgs e)
        {
            Application.Exit();
        }
        
       private   void   textBox1_KeyPress(object   sender,   System.Windows.Forms.KeyPressEventArgs   e)   
       {   
            if   ((e.KeyChar   <   48   ||   e.KeyChar   >   57)   &&   (e.KeyChar   !=   8)  &&  (e.KeyChar  !=0  )  && (e.KeyChar != 46))   
            {   
                 e.Handled   =   true;   
            }   
        }   
    }
}为什么我输入带有小字点的数字后,小数点后面的数却不能参与运算?
比如我输入45.5,乘以10以后就本该是455,但是却输入450
原因?????????????????