[C#]组合框设计windows加减乘除简单计算器应用

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 combox
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
label1.Text = "=";
button1.Text = "选择不同运算符进行计算";
comboBox1.Items.Add("+");
comboBox1.Items.Add("-");
comboBox1.Items.Add("*");
comboBox1.Items.Add("/");
}

private void label1_Click(object sender, EventArgs e)
{

}

private void button1_Click(object sender, EventArgs e)
{
float a, b, c;
a = Convert.ToSingle(textBox1.Text);
b = Convert.ToSingle(textBox2.Text);
if (comboBox1.Text== "+")
{
c = a + b;
textBox3.Text = c.ToString();
}
else if (comboBox1.Text == "-")
{
c = a - b;
textBox3.Text = c.ToString() ;
}
else if (comboBox1.Text == "*")
{
c = a * b;
textBox3.Text = c.ToString();

}
else
{
c = a / b;
textBox3.Text = c.ToString();
}
}

private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
{

}
}
}