通过Stack实现加减乘除

using System;using System.Collections.Generic;using System.Linq;using System.Text;using System.Threading.Tasks;namespace DataStructure{    class StackDemo    {        static void Main(string[] args)        {            //  TreeNodeTest();            string infix = "2+3*4*(6+8)*2";  // 中缀            string suffix = InfixChangeSuffix(infix); // 中缀转后缀            Console.WriteLine("====suffix======" + suffix);            double result = CalcSuffix(suffix.Split(',').ToArray());            Console.WriteLine(result);            Console.ReadLine();        }        /// <summary>        /// 中缀转后缀        /// </summary>        /// <param name="infixExpression">中缀表达式</param>        /// <returns></returns>        static string InfixChangeSuffix(string infixExpression)        {            string suffix = string.Empty;            string completeDigits = string.Empty;            Stack<char> stack = new Stack<char>();            for (int i = 0; i < infixExpression.Length; i++)            {                if (IsOperator(infixExpression[i])) // 是否是运算符                {                    if (!String.IsNullOrWhiteSpace(completeDigits))                    {                        suffix += completeDigits + ",";  // 把前面的数字加入到后缀表达式里                        completeDigits = string.Empty;   // 清空,待下次继续使用                    }                    if (stack.Count > 0)  // 如果栈里有元素，则判断当前符号与栈顶元素的优先级                    {                        char stackTopSymbol;                        if (infixExpression[i] == '(') // 如果是左括号则直接进栈                        {                            stack.Push(infixExpression[i]);                        }                        else if (infixExpression[i] == ')')  // 如果是右括号,则出栈直到遇到左括号为止                        {                            stackTopSymbol = stack.Pop();  // 弹出栈顶元素                            do                            {                                if (stackTopSymbol != '(') suffix += Convert.ToString(stackTopSymbol) + ",";                                if (stack.Count > 0) stackTopSymbol = stack.Pop();                                else break;  // 中缀表达式有异常即四则运算不符合数学规则                            } while (stackTopSymbol != '('); // 直到遇到左括号为止则停止出栈                        }                        else                        {                            stackTopSymbol = stack.Peek();  // 拿栈顶元素出来,但不移除                            int curPriority = Priority(infixExpression[i]);                            int stackTop = Priority(stackTopSymbol);                            if (curPriority <= stackTop)                            {                                do                                {                                    suffix += stackTopSymbol + ",";                                    stack.Pop(); // 栈顶元素优先级高当前符号,则弹出来                                    if (stack.Count > 0)                                    {                                        stackTopSymbol = stack.Peek();// 拿栈顶元素出来,但不移除                                        stackTop = Priority(stackTopSymbol);                                    }                                    else break;  // 原理同上                                } while (curPriority <= stackTop);                            }                            stack.Push(infixExpression[i]);  // 当前的运算符入栈                        }                    }                    else                    {                        stack.Push(infixExpression[i]);                    }                }                else                {                    completeDigits += Convert.ToString(infixExpression[i]);                }            }            suffix += completeDigits + ",";            while (stack.Count > 0)            {                suffix += Convert.ToString(stack.Pop()) + ",";            }            return suffix;        }        /// <summary>        /// 运算符符号优先级        /// </summary>        /// <param name="symbol">运算符符号</param>        /// <returns></returns>        static int Priority(char symbol)        {            switch (symbol)            {                case '*':                case '/':                    return 2;                case '+':                case '-':                    return 1;            }            return -1;        }        static double Calc(double first, double second, char symbol)        {            switch (symbol)            {                case '*':                    return (double)first * second;                case '/':                    return (double)first / second;                case '+':                    return (double)first + second;                case '-':                    return (double)first - second;            }            return 0.0d;        }        static bool IsOperator(char symbol)        {            char[] symbols = { '+', '-', '*', '/', '(', ')' };            return symbols.Contains(symbol);        }        /// <summary>        /// 计算后缀表达式结果        /// </summary>        /// <param name="suffixExpression"></param>        /// <returns></returns>        static double CalcSuffix(string[] suffixExpression)        {            Stack<double> stack = new Stack<double>();            double temp;            for (int i = 0; i < suffixExpression.Length; i++)            {                if (String.IsNullOrWhiteSpace(suffixExpression[i])) break;                if (double.TryParse(suffixExpression[i], out temp))  // 是数字                {                    stack.Push(temp);                }                else  // 是运算符                {                    double rightNum = stack.Pop();                    double leftNum = stack.Pop();                    double result = Calc(leftNum, rightNum, Convert.ToChar(suffixExpression[i]));                    stack.Push(result);                }            }            return stack.Pop();        }    }}