WinForm 制作一个简单的计算器

namespace WindowsFormsApplication6
{
    public partial class Form1 : Form
    {
        //存储上次点击了什么按钮，0代表什么都没有点击，1代表数字按钮，2代表点击了运算符
        private int prev = 0;
        //存储计算的中间结果
        private decimal zjjg = 0;
        //记录上次按得什么运算符
        private string prevysf = "+";

        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e) //输入的数
        {
            //将事件源转换为按钮
            Button btn = sender as Button;
            //替换(文本框内容为0，点击了运算符)
            if (prev == 2 || txtbottom.Text == "0")
            {
                txtbottom.Text = btn.Text;
            }
            //追加(内容不为0，并且上次没有点击运算符)
            else
            {
                txtbottom.Text += btn.Text;
            }
            //点击了按钮数字
            prev = 1;
        }

        private void button4_Click(object sender, EventArgs e) //加减乘除
        {
            //事件源转换为按钮
            Button btn = sender as Button;
            //上次按了数字
            if (prev == 1)
            {
                txttop.Text += txtbottom.Text + btn.Text;//进行显示拼接
                switch (prevysf)
                {
                    case "+":
                        zjjg = zjjg + Convert.ToDecimal(txtbottom.Text); //计算上次运行的结果
                        break;
                    case "-":
                        zjjg = zjjg - Convert.ToDecimal(txtbottom.Text); //计算上次运行的结果
                        break;
                    case "*":
                        zjjg = zjjg * Convert.ToDecimal(txtbottom.Text); //计算上次运行的结果
                        break;
                    case "/":
                        zjjg = zjjg / Convert.ToDecimal(txtbottom.Text); //计算上次运行的结果
                        break;
                }

                txtbottom.Text = zjjg.ToString();
            }
            //上次按了运算符
            else
            {

                if (txttop.Text != "")
                {
                    string s = txttop.Text;
                    s = s.Substring(0, s.Length - 1);
                    s = s + btn.Text;
                    txttop.Text = s;
                }
                else
                {
                    
                    txttop.Text = txtbottom.Text + btn.Text;
                }
            }
            //点击了运算符
            prev = 2;
            //记录下运算符
            prevysf = btn.Text;
        }

        private void button9_Click(object sender, EventArgs e) //清空
        {
            txttop.Text = "";
            txtbottom.Text = "0";
            prevysf = "+";
            prev = 0;
            zjjg = 0;
        }

        private void button11_Click(object sender, EventArgs e) //等于
        {
            //事件源转换为按钮
            Button btn = sender as Button;
                switch (prevysf)
                {
                    case "+":
                        zjjg = zjjg + Convert.ToDecimal(txtbottom.Text); //计算上次运行的结果
                        break;
                    case "-":
                        zjjg = zjjg - Convert.ToDecimal(txtbottom.Text); //计算上次运行的结果
                        break;
                    case "*":
                        zjjg = zjjg * Convert.ToDecimal(txtbottom.Text); //计算上次运行的结果
                        break;
                    case "/":
                        zjjg = zjjg / Convert.ToDecimal(txtbottom.Text); //计算上次运行的结果
                        break;
                }
                txtbottom.Text = zjjg.ToString();
                txttop.Text = "";
                prevysf = "";               
                prev = 2;
        }

        private void button17_Click(object sender, EventArgs e) //回退一个
        {
            string s = txtbottom.Text;
            if (s.Length >1)
            {
                s = s.Substring(0, s.Length - 1);
                txtbottom.Text = s;
            }
            else if(s.Length==1)
            {
                txtbottom.Text = "0";
            }
        }

        private void Form1_Load(object sender, EventArgs e)
        {

        }
    }
}