字符串表达式求值 C#实现

using System;
using System.Collections.Generic;
using System.Windows.Forms;

namespace ExpressionResult1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
        //建立一个数栈和一个操作符栈
        Stack<int> numberStack = new Stack<int>();
        Stack<char> operatorStack = new Stack<char>();

        private void button1_Click(object sender, EventArgs e)
        {
            //在表达式前后加开始和结束标识符
            string expressin = "#" + textBox1.Text + "#";
            bool label = false;//标识是否出现连续的数字字符
            foreach (char ch in expressin)
            {
                if (ch >= '0' && ch <= '9')//数字入栈
                {
                    if (label == true)
                    {
                        int temp = numberStack.Pop();
                        temp = temp * 10 + int.Parse(ch.ToString());
                        numberStack.Push(temp);
                    }
                    else
                    {
                        numberStack.Push(int.Parse(ch.ToString()));
                        label = true;
                    }
                }
                else
                {
                    if (operatorStack.Count == 0)//将开始标识符入栈
                    {
                        operatorStack.Push(ch);
                    }
                    else
                    {
                        label = false;
                        string priority = GetPriority(ch);
                        while(priority == "outOperator")//操作符出栈，并计算前后两个数
                        {
                            int num1 = numberStack.Pop();
                            int num2 = numberStack.Pop();
                            char oper = operatorStack.Pop();
                            int result = GetResult(num1 ,num2 ,oper);
                            numberStack.Push(result );

                            priority = GetPriority(ch);
                        }
                        if (priority == "inOperator")//操作符进栈
                        {
                            operatorStack.Push(ch);
                        }
                        else //操作符直接弹出
                        {
                            operatorStack.Pop();
                        }
                    }
                }
            }

            textBox2.Text = numberStack.Pop().ToString();

        }

        private string GetPriority(char outChar)//比较栈外和栈内两个操作符的优先级
        {
            char inChar = operatorStack.Peek();
            switch (outChar)
            {
                case '+':
                case '-':
                    switch (inChar)
                    {
                        case '+':
                        case '-':                          
                        case '*':
                        case '/':                    
                          return "outOperator";  
                        case '(':
                        case '#':
                          return "inOperator";
                    }
                    break;
                case '*':
                case '/':
                    switch (inChar)
                    {
                        case '+':
                        case '-':
                        case '(':
                        case '#':
                            return "inOperator";
                        case '*':
                        case '/':
                            return "outOperator";
                    }
                    break;
                case '(':
                    return "inOperator";
                case ')':
                    switch (inChar)
                    {
                        case '(':
                            return "abandonOperator";
                        default :
                            return "outOperator";
                    }                   
                case '#':
                    switch (inChar)
                    {
                        case '#':
                            return "abandonOperator";
                        default :
                            return "outOperator";
                    }
                default :
                    throw new Exception("包含非法字符！");
            }
            return "";
        }

        private int GetResult(int num1, int num2, char oper)//根据操作符计算两个数
        {
            int result = 0;
            switch (oper)
            {
                case '+':
                    result = num2 + num1;
                    break;
                case '-':
                    result = num2 - num1;
                    break;
                case '*':
                    result = num2 * num1;
                    break;
                case '/':
                    if (num1==0)
                    {
                        throw new Exception();
                    }
                    result = num2 / num1;
                    break;
                default :
                    result = 0;
                    break;
            }
            return result;

        }
    }
}