using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Text.RegularExpressions;
using System.Threading.Tasks;

namespace CStack
{
    class example_01
    {
        static void Main() {
            string expression = "5 + 10 + 15 + 20";
            Stack nums = new Stack();
            Stack ops = new Stack();

            Caluate(nums, ops, expression);

            Console.WriteLine(nums.Pop());//最终结果
            Console.Read();
        }


        static bool IsNumber(string input) {
            bool flag = true;
            string pattern = (@"^\d+$");
            Regex valodate = new Regex(pattern);//验证 表示不可变的正则表达式
            if (!valodate.IsMatch(input))
            {
                flag = false;
            }
            return flag;
        }

        static void Caluate(Stack N,Stack O, string exp) {
            string ch, token="";
            for (int i = 0; i < exp.Length; i++)
            {
                ch = exp.Substring(i, 1);
                if (IsNumber(ch))
                    token += ch;//获取数字
                if (ch==" "||i==(exp.Length-1))
                {
                    if (IsNumber(token))//是数字
                    {
                        N.Push(token);
                        token = "";
                    }
                }
                else if (ch=="+"||ch=="-"||ch=="*" || ch == "/")           
                    O.Push(ch);//操作符号

                if (N.Count==2)//满足两个就运算
                    Compute(N,O);            
            }

        }

        /// <summary>
        /// 运算
        /// </summary>
        /// <param name="N"></param>
        /// <param name="O"></param>
        static void Compute(Stack N, Stack O) {
            int oper1, oper2;//俩个操作数字
            string oper;//符号
            oper1 =Convert.ToInt32( N.Pop());
            oper2 = Convert.ToInt32(N.Pop());
            oper = Convert.ToString(O.Pop());

            switch (oper) {

                case "+":
                    N.Push(oper1+oper2);
                    break;
                case "-":
                    N.Push(oper1 - oper2);
                    break;
                case "*":
                    N.Push(oper1 * oper2);
                    break;
                case "/":
                    N.Push(oper1 /oper2);
                    break;
                default:
                    break;
            }

        }
    }
}