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

namespace Calculator
{
    class Program
    {

        static void Main(string[] args)
        {
            try
            {
                double x;
                double y;

                double res = 0;

                Console.BackgroundColor = ConsoleColor.Black;
                Console.ForegroundColor = ConsoleColor.DarkGreen;

                Console.WriteLine("Please enter a number: \n");
                x = double.Parse(Console.ReadLine());

                for (;;)
                {
                    Console.WriteLine("\n Please enter another number: \n");
                    y = double.Parse(Console.ReadLine());
                    Console.WriteLine();
                    Console.WriteLine("\nChoose your operation method (+,-,*,/)\n");
                    Boolean eingabe = true;
                    switch (Console.ReadLine())

                    {
                        case "+":
                            {
                                double sum = Add(x, y);
                                Console.WriteLine("\nThe sum of the operation is: " + sum + "\n");
                                res = sum;
                                break;
                            }

                        case "-":
                            {
                                double dif = Sub(x, y);
                                Console.WriteLine("\nThe difference of the operation is: " + dif + "\n");
                                res = dif;
                                break;
                            }

                        case "*":
                            {
                                double mult = Mult(x, y);
                                Console.WriteLine("\nThe product of the operation is: " + mult + "\n");
                                res = mult;
                                break;
                            }

                        case "/":
                            {
                                double div = Div(x, y);
                                Console.WriteLine("\nThe quotient of the operation is: " + div + "\n");
                                res = div;
                                break;
                            }

                        default:
                            {
                                Console.WriteLine("\nYou did not enter a valid operator!\n");
                                break;
                            }
                    }

                    Console.WriteLine("\nDo you want to use the previous result in the next operation? Y/N\n");
                    while (eingabe)
                    {
                        string prev = Console.ReadLine();
                        if (prev == "Y" || prev == "N")
                        {
                            if (prev == "Y")
                            {
                                eingabe = false;
                                x = res;

                            }
                            else
                            {
                                eingabe = false;
                                Console.WriteLine("Please enter a number: \n");
                                x = double.Parse(Console.ReadLine());
                            }
                        }
                    }
                }
            } catch (Exception ex)

            {
                Console.WriteLine("\n" + ex.Message + "\n");

            }
        }

        static double Add(double x, double y)
        {
            return x + y;
        }

        static double Sub(double x, double y)
        {
            return x - y;
        }

        static double Mult(double x, double y)
        {
            return x * y;
        }

        static double Div(double x, double y)
        {
            if (y == 0)
            {
                throw new Exception("\nThe quotient of the operation is: infinity (Cannot divide by 0!)\n");
            }
            else
            {
                return x / y;
            }
        }

    }
}