自制c#简易计算器

这是一个课堂作业，我觉得作为一个简易的计算器不需要态度复杂的东西，可能还有一些bug，有空再慢慢加强。

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.Speech;
using System.Speech.Synthesis;

namespace WindowsFormsApplication1
{
public partial class Form1 : Form
{
SpeechSynthesizer sp = new SpeechSynthesizer();
public Form1()
{
InitializeComponent();
}

private void Form1_Load(object sender, EventArgs e)
{
this.Text = "简易计算器";
}

private void button1_Click(object sender, EventArgs e)
{
if (textBox1.Text != string.Empty && textBox2.Text != string.Empty)
{
double a = double.Parse(textBox1.Text);
double b = double.Parse(textBox2.Text);
textBox3.Text = String.Format("结果是{0}", (a + b));
sp.SpeakAsync(textBox3.Text);
}
else
{
textBox3.Text = "输入条件不足";
}
}

private void button2_Click(object sender, EventArgs e)
{
if (textBox1.Text != string.Empty && textBox2.Text != string.Empty)
{
double a = double.Parse(textBox1.Text);
double b = double.Parse(textBox2.Text);
textBox3.Text = String.Format("结果是{0}", (a - b));
sp.SpeakAsync(textBox3.Text);
}
else
{
textBox3.Text = "输入条件不足";
}
}

private void button3_Click(object sender, EventArgs e)
{
if (textBox1.Text != string.Empty && textBox2.Text != string.Empty)
{
double a = double.Parse(textBox1.Text);
double b = double.Parse(textBox2.Text);
textBox3.Text = String.Format("结果是{0}", (a*b));
sp.SpeakAsync(textBox3.Text);
}
else
{
textBox3.Text = "输入条件不足";
}
}

private void button4_Click(object sender, EventArgs e)
{
if (textBox1.Text != string.Empty && textBox2.Text != string.Empty)
{
double a = double.Parse(textBox1.Text);
double b = double.Parse(textBox2.Text);
textBox3.Text = String.Format("结果是{0}", (a / b));
sp.SpeakAsync(textBox3.Text);
}
else
{
textBox3.Text = "输入条件不足";
}
}

private void button5_Click(object sender, EventArgs e)
{
if (textBox1.Text != string.Empty && textBox2.Text != string.Empty)
{
double a = double.Parse(textBox1.Text);
textBox3.Text = String.Format("结果是{0}", (Math.Sqrt(a)));
sp.SpeakAsync(textBox3.Text);}
else
{
textBox3.Text = "输入条件不足";
}

}
}
}