adding a dot in a calculator display

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C#

Hello!
I'm doing a C# tutorial (homeandlearn.co.uk) and i'm currently making a calculator.
However, I've gotten to the point where I'll make the calculator accept "dots" and I dont know what "symbol" to use for just dot... Alright, here's the code:

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;

namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
        double total1 = 0;
        double total2 = 0;
        private void button1_Click(object sender, EventArgs e)
        {
            textBox1.Text = textBox1.Text + button1.Text;
        }

        private void textBox1_TextChanged(object sender, EventArgs e)
        {

        }

        private void button2_Click(object sender, EventArgs e)
        {
            textBox1.Text = textBox1.Text + button2.Text;
        }

        private void button3_Click(object sender, EventArgs e)
        {
            textBox1.Text = textBox1.Text + button3.Text;
        }

        private void button9_Click(object sender, EventArgs e)
        {
            textBox1.Text = textBox1.Text + button9.Text;
        }

        private void button6_Click(object sender, EventArgs e)
        {
            textBox1.Text = textBox1.Text + button6.Text;
        }

        private void button5_Click(object sender, EventArgs e)
        {
            textBox1.Text = textBox1.Text + button5.Text;
        }

        private void button4_Click(object sender, EventArgs e)
        {
            textBox1.Text = textBox1.Text + button4.Text;
        }

        private void button7_Click(object sender, EventArgs e)
        {
            textBox1.Text = textBox1.Text + button7.Text;
        }

        private void button8_Click(object sender, EventArgs e)
        {
            textBox1.Text = textBox1.Text + button8.Text;
        }

        private void button0_Click(object sender, EventArgs e)
        {
            textBox1.Text = textBox1.Text + button0.Text;
        }

        private void btnClear_Click(object sender, EventArgs e)
        {
            textBox1.Clear();
        }

        private void btnPlus_Click(object sender, EventArgs e)
        {
            total1 = total1 + double.Parse(textBox1.Text);
            textBox1.Clear();
        }

        private void btnEquals_Click(object sender, EventArgs e)
        {
            total2 = total1 + double.Parse(textBox1.Text);
            textBox1.Text = total2.ToString();
            total1 = 0;
        }

        private void btnPoint_Click(object sender, EventArgs e)
        {
            textBox1.Text = textBox1.Text + ".";
        }
    }
}

Please do note that the btn point is at the end.

Again sorry for the noobish questions at a such well established place as this.
[b]At its current state, the program crashes whenever i press +, or =, [/b]


The lesson said this: "You have not yet written any code for the btnPoint button. This means that you can't have numbers like 10.5 or 36.7 in your additions. Write code to solve this. (Hint: you only need one line of code.)"





error i get:

See the end of this message for details on invoking
just-in-time (JIT) debugging instead of this dialog box.

************** Exception Text **************
System.FormatException: Input string was not in a correct format.
   at System.Number.ParseDouble(String value, NumberStyles options, NumberFormatInfo numfmt)
   at WindowsFormsApplication1.Form1.btnPlus_Click(Object sender, EventArgs e) in C:\Users\Weidrup\AppData\Local\Temporary Projects\WindowsFormsApplication1\Form1.cs:line 82
   at System.Windows.Forms.Control.OnClick(EventArgs e)
   at System.Windows.Forms.Button.OnClick(EventArgs e)
   at System.Windows.Forms.Button.OnMouseUp(MouseEventArgs mevent)
   at System.Windows.Forms.Control.WmMouseUp(Message& m, MouseButtons button, Int32 clicks)
   at System.Windows.Forms.Control.WndProc(Message& m)
   at System.Windows.Forms.ButtonBase.WndProc(Message& m)
   at System.Windows.Forms.Button.WndProc(Message& m)
   at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
   at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
   at System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)


************** Loaded Assemblies **************
mscorlib
    Assembly Version: 4.0.0.0
    Win32 Version: 4.0.30319.225 (RTMGDR.030319-2200)
    CodeBase: file:///C:/Windows/Microsoft.NET/Framework/v4.0.30319/mscorlib.dll
----------------------------------------
WindowsFormsApplication1
    Assembly Version: 1.0.0.0
    Win32 Version: 1.0.0.0
    CodeBase: file:///C:/Users/Weidrup/AppData/Local/Temporary%20Projects/WindowsFormsApplication1/bin/Release/WindowsFormsApplication1.exe
----------------------------------------
System.Windows.Forms
    Assembly Version: 4.0.0.0
    Win32 Version: 4.0.30319.1 built by: RTMRel
    CodeBase: file:///C:/Windows/Microsoft.Net/assembly/GAC_MSIL/System.Windows.Forms/v4.0_4.0.0.0__b77a5c561934e089/System.Windows.Forms.dll
----------------------------------------
System.Drawing
    Assembly Version: 4.0.0.0
    Win32 Version: 4.0.30319.1 built by: RTMRel
    CodeBase: file:///C:/Windows/Microsoft.Net/assembly/GAC_MSIL/System.Drawing/v4.0_4.0.0.0__b03f5f7f11d50a3a/System.Drawing.dll
----------------------------------------
System
    Assembly Version: 4.0.0.0
    Win32 Version: 4.0.30319.1 built by: RTMRel
    CodeBase: file:///C:/Windows/Microsoft.Net/assembly/GAC_MSIL/System/v4.0_4.0.0.0__b77a5c561934e089/System.dll
----------------------------------------

************** JIT Debugging **************
To enable just-in-time (JIT) debugging, the .config file for this
application or computer (machine.config) must have the
jitDebugging value set in the system.windows.forms section.
The application must also be compiled with debugging
enabled.

For example:

<configuration>
    <system.windows.forms jitDebugging="true" />
</configuration>

When JIT debugging is enabled, any unhandled exception
will be sent to the JIT debugger registered on the computer
rather than be handled by this dialog box.