Calculator

namespace Calculator
{
    using System;
    using System.IO;

    static class Calculator
    {
        static void Main()
        {
            Console.WriteLine("Content-Type: text/html\r\n");
            string htmlContent = File.ReadAllText("../www/calculator.html");
            Console.WriteLine(htmlContent);
            string post = Console.ReadLine();
            if (post != null)
            {
                string[] postSplited = post.Split(new[] { '&', '=' }, StringSplitOptions.RemoveEmptyEntries);
                double firstNum = double.Parse(postSplited[1]);
                string operation = postSplited[3];
                double secondNum = double.Parse(postSplited[5]);

                switch (operation)
                {
                    case "%2B": // + sign
                        Console.WriteLine("Result: " + (firstNum + secondNum));
                        break;
                    case "-": // - sign
                        Console.WriteLine("Result: " + (firstNum - secondNum));
                        break;
                    case "*": // * sign
                        Console.WriteLine("Result: " + (firstNum * secondNum));
                        break;
                    case "%2F": // / sign
                        Console.WriteLine("Result: " + (firstNum / secondNum));
                        break;
                    default:
                        Console.WriteLine("Invalid sign!");
                        break;
                }
            }
        }
    }
}