//Microsoft (R) Visual C# Compiler version 3.4.0-beta4-19562-05 (ff930dec)

//Copyright (C) Microsoft Corporation. All rights reserved.

​

using System;

using System.Collections.Generic;

​

namespace Rextester

{

    public class Program

    {

        public static void Main(string[] args)

        {

            while(true)

            {

                Console.WriteLine("請輸入四則運算式：");

                string input = Console.ReadLine();

​

                try

                {

                    int result = Calculate(input);

                    Console.WriteLine("計算結果：" + result);

                }

                catch (Exception ex)

                {

                    Console.WriteLine("計算錯誤：" + ex);

                }

            }

        }

​

        static int Calculate(string input)

        {

            // 移除空格

            input = input.Replace(" ", "");

​

            // 將運算式轉換成後序表示法（Reverse Polish Notation, RPN）

            string rpn = ConvertToRPN(input);

            Console.WriteLine(rpn);

​

            // 使用堆疊來計算 RPN 運算式

            return EvaluateRPN(rpn);

        }

​

        static string ConvertToRPN(string input)

        {

            // 初始化後序表示法和運算子堆疊

            string rpn = "";

            Stack<char> operators = new Stack<char>();

​

            // 定義運算符的優先順序

            Dictionary<char, int> precedence = new Dictionary<char, int>

            {

                { '+', 1 },

                { '-', 1 },

                { 'x', 2 },

                { '*', 2 },

                { '/', 2 }

            };

​

            // 將中序表示法轉換成後序表示法

            foreach (char ch in input)

            {

                if (char.IsDigit(ch))

                {

                    rpn += ch;

                }

                else if (precedence.ContainsKey(ch))

                {

                    while (operators.Count > 0 && precedence[operators.Peek()] >= precedence[ch])

                    {

                        rpn += operators.Pop();

                    }

                    operators.Push(ch);

                }

                else if (ch == '(')

                {

                    operators.Push(ch);

                }

                else if (ch == ')')

                {

                    while (operators.Count > 0 && operators.Peek() != '(')

                    {

                        rpn += operators.Pop();

                    }

                    operators.Pop(); // 移除左括號

                }

                else

                {

                    throw new ArgumentException("輸入包含無效字符。");

                }

            }

​

            while (operators.Count > 0)

            {

                rpn += operators.Pop();

            }

​

            return rpn;

        }

​

        static int EvaluateRPN(string rpn)

        {

            Stack<int> operands = new Stack<int>();

​

            foreach (char ch in rpn)

            {

                if (char.IsDigit(ch))

                {

                    operands.Push(int.Parse(ch.ToString()));

                }

                else

                {

                    int b = operands.Pop();

                    int a = operands.Pop();

​

                    switch (ch)

                    {

                        case '+':

                            operands.Push(a + b);

                            break;

                        case '-':

                            operands.Push(a - b);

                            break;

                        case 'x':

                        case '*':

                            operands.Push(a * b);

                            break;

                        case '/':

                            if (b == 0)

                            {

                                throw new DivideByZeroException("除數不能為零。");

                            }

                            operands.Push(a / b);

                            break;

                    }

                }

            }

​

            return operands.Pop();

        }

    }

}