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I have an assignment to create a postfix notation from the infix. I got the code working properly and i have a string of the postfix notation, however I'm not sure how to get the answer from it. Is there a .NET method I can call? I tried Googling the problem and can only find how to change it to post fix.

Any help is much appreciated.

Update I needed to find the answer to an expression like: 12+3-4+5-

I was hoping to find an easier way to do this but I did not so i wrote my own method to. I will post it in 8 hours when i am allowed to.

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2 回答 2

3

后缀是字符串中的表达式，例如“10 9 + 7 % 3 -”

postfix = postfix.Trim();
                string[] ans = postfix.Split(' ');
                Stack<int> eval = new Stack<int>();
                for (int x = 0; x < ans.Length; x++)
                {
                    if ("*+%/-".Contains(ans[x]))
                    {
                        int temp1;
                        int temp2;

                        switch (ans[x])
                        {
                            case ("*"):
                                eval.Push(eval.Pop() * eval.Pop());
                                break;
                            case "-":
                                temp1 = eval.Pop();
                                temp2 = eval.Pop();
                                eval.Push(temp2 - temp1);
                                break;
                            case "%":
                                temp1 = eval.Pop();
                                temp2 = eval.Pop();
                                eval.Push(temp2 % temp1);
                                break;
                            case "+":
                                eval.Push(eval.Pop() + eval.Pop());
                                break;
                            case "/":
                                temp1 = eval.Pop();
                                temp2 = eval.Pop();
                                eval.Push(temp2 / temp1);
                                break;
                        }

                    }
                    else
                        eval.Push(Convert.ToInt32(ans[x]));
                }

//过早地切断代码。在 for 语句执行完毕后，答案将是 int answer = eval.Pop();

于 2012-04-05T15:54:25.540 回答
0 
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Collections;

namespace pof
{
    class eva
    {
        public string po;
        public string answer;
        Stack i = new Stack();
        public void e()
        {
            int a, b, ans;
            for (int j = 0; j < po.Length; j++)
            {
                String c = po.Substring(j, 1);
                if (c.Equals ("*"))
                {
                    String sa = (String)i.Pop();
                    String sb = (String)i.Pop();
                    a = Convert.ToInt32(sb); 
                    b = Convert.ToInt32(sa);
                    ans = a * b;
                    i.Push(ans.ToString());

                }
                else if (c.Equals("/"))
                {
                    String sa = (String)i.Pop();
                    String sb = (String)i.Pop();
                    a = Convert.ToInt32(sb);
                    b = Convert.ToInt32(sa);
                    ans = a / b;
                    i.Push(ans.ToString());
                }
                else if (c.Equals("+"))
                {
                    String sa = (String)i.Pop();
                    String sb = (String)i.Pop();
                    a = Convert.ToInt32(sb);
                    b = Convert.ToInt32(sa);
                    ans = a + b;
                    i.Push(ans.ToString());

                }
                else if (c.Equals("-"))
                {
                    String sa = (String)i.Pop();
                    String sb = (String)i.Pop();
                    a = Convert.ToInt32(sb);
                    b = Convert.ToInt32(sa);
                    ans = a - b;
                    i.Push(ans.ToString());

                }
                else
                {
                    i.Push(po.Substring(j, 1));
                }
            }
          answer=(String)i.Pop();
        }
    }
    class Program
    {
        static void Main(string[] args)
        {
            eva e1 = new eva();
            Console.WriteLine("enter any postfix expression");
            e1.po = Console.ReadLine();
            e1.e();
            Console.WriteLine("\n\t\tpostfix evaluation:  " + e1.answer);
            Console.ReadKey();
        }
    }
}
于 2014-11-16T18:58:44.857 回答