用Visual Studio 2019做一个计算器
1.创建新项目

模式选择window窗体应用

项目名称calcular

开始做计算器

可从左边的工具箱拖拽需要用的组件到Form1上，我们用Button和TextBox两个组件来做

Form1.cs记录的是可视化界面的源码情况，可在里面修改代码

如果不小心关闭了一些界面可在右上角搜索框搜索，

右边显示的是该组件的属性，可在里面规定字体一类，该图是textBox属性

设计好界面后去Form1.cs修改代码，编辑文本组件相应的事件（途中C是归零）
运行代码，形成可使用的计算器
思路
因为数据结构之前学过堆栈计算后缀表达式，故
我设计的计算器是先用string s记录textBox中的字符串，然后将中缀表达式转换成后缀表达式，再计算后缀表达式


原理
中缀表达式s转换为后缀表达式s1然后计算
用string s1记录转换成功后的后缀表达式
一、中缀->后缀
遍历字符串s
1.遇到数字或小数点，直接放入s1(加入空格是为了区分数字，防止如1和2放在一起成了12)
代码

 while (i<s.Length &&(s[i] >= '0' && s[i] <= '9'||s[i]=='.'))
 {
 	s1 += s[i];
   i++;
 }
    i--;
   s1 += " ";

2.遇到运算符，将运算符与栈顶元素比较，若优先级高于栈顶运算符则压入栈，若优先级低于栈顶运算符，则将栈顶运算符弹出（即用s1记录）再比较
代码

   		 if (s[i] == '+' || s[i] == '-' || s[i] == '*' || s[i] == '/')
               {
                   if (op.Count == 0 || dic[s[i]] > dic[op.Peek()])
                   {
                       op.Push(s[i]);//栈为空，或者s[i]优先级大于栈顶,入栈
                   }
                   else
                   {
                       Stack<Char> op1 = new Stack<Char>();
                       while (op.Count > 0 && dic[s[i]] <= dic[op.Peek()])//s[i]优先级小于等于栈顶元素
                       {
                           s1 += op.Peek() + " ";
                           op.Pop();
                       }
                       op.Push(s[i]);
                   }

字符串s遍历完成，s1记录运算符顺序

			while (op.Count > 0)
            {
                s1 += op.Peek();
                op.Pop();
            }

二、计算后缀表达式
令s=s1，遍历s
Stack num = new Stack();
1.遇到数字直接入栈
2.遇到运算符，出栈num第一个和第二个数来运算，并将运算结果入栈
3.最后输出num中的结果
代码

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace Calculator
{
    public partial class C : Form
    {
        public C()
        {
            InitializeComponent();
        }
        Double LeftNum, Rightnum, Result;
        String Flag;
        private void Form1_Load(object sender, EventArgs e)
        {

        }
        private void textBox1_TextChanged(object sender, EventArgs e)
        {

        }

        private void button1_Click(object sender, EventArgs e)
        {
            textBox1.Text += "1";
        }


        private void button2_Click(object sender, EventArgs e)
        {
            textBox1.Text += "2";
        }

        private void button3_Click(object sender, EventArgs e)
        {
            textBox1.Text += "3";
        }

        private void button4_Click(object sender, EventArgs e)
        {
            textBox1.Text += "4";
        }

        private void button5_Click(object sender, EventArgs e)
        {
            textBox1.Text += "5";
        }

        private void button6_Click(object sender, EventArgs e)
        {
            textBox1.Text += "6";
        }

        private void button7_Click(object sender, EventArgs e)
        {
            textBox1.Text += "7";
        }
        private void button8_Click(object sender, EventArgs e)
        {
            textBox1.Text += "8";
        }
        private void button9_Click(object sender, EventArgs e)
        {
            textBox1.Text += "9";
        }
        private void button_Add_Click(object sender, EventArgs e)
        {
            textBox1.Text += "+";
        }
        private void button_multiply_Click(object sender, EventArgs e)
        {
            textBox1.Text += "*";
        }
        private void Divide_Click(object sender, EventArgs e)
        {
            textBox1.Text += "/";
        }

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

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

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

        private void button_equal_Click(object sender, EventArgs e)
        {
            String s = textBox1.Text;
            String s1 = "";
            Stack<Char> op = new Stack<Char>();
            Dictionary<char, int> dic = new Dictionary<char, int>();
            dic['+'] = dic['-'] = 1;
            dic['*'] = dic['/'] = 2;
            for (int i = 0; i < s.Length; i++)//中缀表达式转换后缀表达式
            {
                if (s[i] == '+' || s[i] == '-' || s[i] == '*' || s[i] == '/')
                {
                    if (op.Count == 0 || dic[s[i]] > dic[op.Peek()])
                    {
                        op.Push(s[i]);//栈为空，或者s[i]优先级大于栈顶,入栈
                    }
                    else
                    {
                        Stack<Char> op1 = new Stack<Char>();
                        while (op.Count > 0 && dic[s[i]] <= dic[op.Peek()])//s[i]优先级小于等于栈顶元素
                        {
                            s1 += op.Peek() + " ";
                            op.Pop();
                        }
                        op.Push(s[i]);
                    }
                }
                else
                {
                    while (i<s.Length &&(s[i] >= '0' && s[i] <= '9'||s[i]=='.'))
                    {
                        s1 += s[i];
                        i++;
                    }
                    i--;
                    s1 += " ";
                }
            }
            while (op.Count > 0)
            {
                s1 += op.Peek();
                op.Pop();
            }

            //转换为后缀表达式s1
            s = s1;
            Stack<Double> num = new Stack<double>();
            for (int i = 0; i < s.Length; i++)
            {
                if(s[i]=='+'||s[i]=='-'||s[i]=='*'||s[i]=='/')
                {
                    double a = num.Peek();
                    num.Pop();
                    double b = num.Peek();
                    num.Pop();
                    if (s[i] == '/') num.Push(b / a);
                    else if (s[i] == '-') num.Push(b - a);
                    else if (s[i] == '+') num.Push(a + b);
                    else if (s[i] == '*') num.Push(a * b);

                }
              else if(s[i]!=' ')
             {
                string sm = "";
                 while (i < s.Length && (s[i] >= '0' && s[i] <= '9' || s[i] == '.'))
                    {
                        sm += s[i];
                        i++;
                 }
                    i--;
                    Double d = Convert.ToDouble(sm);
                    num.Push(d);
             }
            }
            s1 = Convert.ToString(num.Peek());
            textBox1.Text = s1;
        }
    }
}