Prefix.cs

using System;
using System.Collections.Generic;

namespace Prefix
{
    static class Program
    {
        private static void Main(string[] args)
        {
            Console.WriteLine("İşlemi giriniz:");
            string ifade = Console.ReadLine();
            Console.WriteLine("Sonuc: " + HesaplaOnEkliIfade(ifade));
            Console.ReadLine();
        }
        private static double HesaplaOnEkliIfade(string onEkliIfade)
        {
            string[] degerler = onEkliIfade.Split(' ');
            Stack<int> islemYigini = new Stack<int>();

            for (int i = degerler.Length - 1; i >= 0; i--)
            {
                if (OperatorKontrol(degerler[i]))
                {
                    int islem1 = islemYigini.Pop();
                    int islem2 = islemYigini.Pop();

                    switch (degerler[i])
                    {
                        case "+":
                            islemYigini.Push(islem1 + islem2);
                            break;
                        case "-":
                            islemYigini.Push(islem1 - islem2);
                            break;
                        case "*":
                            islemYigini.Push(islem1 * islem2);
                            break;
                        case "/":
                            islemYigini.Push(islem1 / islem2);
                            break;
                    }
                }
                else
                {
                    islemYigini.Push(int.Parse(degerler[i]));
                }
            }

            return islemYigini.Pop();
        }

        private static bool OperatorKontrol(string op)
        {
            return "+" == op || "-" == op || "*" == op || "/" == op;
        }

    }
}