11-12 計算機 正確

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 string str = ""; //把數字鍵字串存起來
        public double ans = 0;//佔存變數  
        public int how = 0;//判斷按下+ - * /
   

        public Form1()
        {
            InitializeComponent();
        }
        private void Form1_Load(object sender, EventArgs e)
        {
        }
        private void button16_Click(object sender, EventArgs e)
        {
            str = "";    //顯示0
            textBox1.Text = "0";

        }
        private void button1_Click(object sender, EventArgs e)
        {
            if (str == "0") { str = ""; }//數字鍵1
            str += "1";
            textBox1.Text = str;//顯示字串內容

        }
        private void button2_Click(object sender, EventArgs e)
        {
            if (str == "0") { str = ""; }//數字鍵2
            str += "2";
            textBox1.Text = str;

        }
        private void button3_Click(object sender, EventArgs e)
        {
            if (str == "0") { str = ""; }//數字鍵3
            str += "3";
            textBox1.Text = str;
        }
        private void button4_Click(object sender, EventArgs e)
        {
            if (str == "0") { str = ""; }
            str += "4";
            textBox1.Text = str;
        }
        private void button5_Click(object sender, EventArgs e)
        {
            if (str == "0") { str = ""; }
            str += "5";
            textBox1.Text = str;
        }
        private void button6_Click(object sender, EventArgs e)
        {
            if (str == "0") { str = ""; }
            str += "6";
            textBox1.Text = str;
        }
        private void button7_Click(object sender, EventArgs e)
        {
            if (str == "0") { str = ""; }
            str += "7";
            textBox1.Text = str;
        }
        private void button8_Click(object sender, EventArgs e)
        {
            if (str == "0") { str = ""; }
            str += "8";
            textBox1.Text = str;
        }
        private void button9_Click(object sender, EventArgs e)
        {
            if (str == "0") { str = ""; }
            str += "9";
            textBox1.Text = str;
        }
        private void button15_Click(object sender, EventArgs e)
        {
      
            if (str != "")//點擊=鍵
            { 
               if (how == 1) { ans += Convert.ToDouble(str); }//轉換成浮點數
               else if (how == 2) { ans -= Convert.ToDouble(str); }
               else if (how == 3) { ans *= Convert.ToDouble(str); }
               else if (how == 4) { ans /= Convert.ToDouble(str); }
               else if (ans == 0) { ans = Convert.ToDouble(str); }
             
               else ans = Convert.ToDouble(str);
            }

            how = 0;//再儲存使用者所按下的運算元

            str = Convert.ToString(ans);
          
                    
            textBox1.Text = str;
            label1.Text = "=";

        }
        private void button11_Click(object sender, EventArgs e)
        {
            if (how == 1)
            { if (str == "") { str = "0"; };ans += Convert.ToDouble(str); }
            else if (how == 2)
            { if (str == "") { str = "0"; };ans -= Convert.ToDouble(str); }
            else if (how == 3)
            { if (str == "") { str = "1"; };ans *= Convert.ToDouble(str); }
            else if (how == 4)
            { if (str == "") { str = "1"; };ans /= Convert.ToDouble(str); }
            else if (how == 0)
            { if (str == "") { str = "0"; } ans = Convert.ToDouble(str); }
            textBox1.Text = Convert.ToString(ans);

            how = 1;
          
            str = "";

        }
        private void button12_Click(object sender, EventArgs e)
        {
            if (how == 1)
            { if (str == "") { str = "0"; };ans += Convert.ToDouble(str); }
            else if (how == 2)
            { if (str == "") { str = "0"; };ans -= Convert.ToDouble(str); }
            else if (how == 3)
            { if (str == "") { str = "1"; };ans *= Convert.ToDouble(str); }
            else if (how == 4)
            { if (str == "") { str = "1"; };ans /= Convert.ToDouble(str); }
            else if (how == 0)
            { if (str == "") { str = "0"; } ans = Convert.ToDouble(str); }
            textBox1.Text = Convert.ToString(ans);

            how = 2;
          
            str = "";

        }
        private void button13_Click(object sender, EventArgs e)
        {
            if (how == 1)
            { if (str == "") { str = "0"; };ans += Convert.ToDouble(str); }
            else if (how == 2)
            { if (str == "") { str = "0"; };ans -= Convert.ToDouble(str); }
            else if (how == 3)
            { if (str == "") { str = "1"; };ans *= Convert.ToDouble(str); }
            else if (how == 4)
            { if (str == "") { str = "1"; };ans /= Convert.ToDouble(str); }
            else if (how == 0)
            { if (str == "") { str = "0"; } ans = Convert.ToDouble(str); }
            textBox1.Text = Convert.ToString(ans);

            how = 3;
           
            str = "";

        }
        private void button14_Click(object sender, EventArgs e)
        {
            if (how == 1)
            { if (str == "") { str = "0"; };ans += Convert.ToDouble(str); }
            else if (how == 2)
            { if (str == "") { str = "0"; };ans -= Convert.ToDouble(str); }
            else if (how == 3)
            { if (str == "") { str = "1"; };ans *= Convert.ToDouble(str); }
            else if (how == 4)
            { if (str == "") { str = "1"; };ans /= Convert.ToDouble(str); }
            else if (how == 0)
            { if (str == "") { str = "0"; } ans = Convert.ToDouble(str); }
            textBox1.Text = Convert.ToString(ans);

            how = 4;
           
            str = "";

        }
        private void button10_Click(object sender, EventArgs e)
        {
            if (str == "0") { str = ""; }
            str += "0";
        }
    }
}