using System;

// using System.Collections.Generic;

// using System.Linq;

// using System.Text;

// using System.Threading.Tasks;

​

namespace Calculator

{

    internal class Program

    {

        public class Calculations

        {

            public static double Addition(double num1, double num2)

            {

                return num1 + num2;

            }

            public static double Subtraction(double num1, double num2)

            {

                return num1 - num2;

            }

            public static double Multiplication(double num1, double num2)

            {

                return num1 * num2;

            }

            public static double Division(double num1, double num2)

            {

                return num1 / num2;

            }

​

            public static double InsertNum()

            {

                double number;

                Console.WriteLine("Insert number: ");

                while (!double.TryParse(Console.ReadLine(), out number))

                {

                    Console.WriteLine("Not correct input. Try again: ");

                }

                return number;

            }

​

            public static string InsertMath()

            {

                Console.WriteLine("Inser math operation, q or c: ");

                string operation = Console.ReadLine();

                while (operation != "+" && operation != "-" && operation != "*" && operation != "/" && operation != "c" && operation != "q")

                {

                    Console.WriteLine("Unknown operation, try again: ");

                    operation = Console.ReadLine();

                }

                return operation;

            }

            public static double GetResult(double number1, double number2, string math)

            {

                switch (math)

                {

                    case "+":

                        return Addition(number1, number2);

                    case "-":

                        return Subtraction(number1, number2);

                    case "*":

                        return Multiplication(number1, number2);

                    case "/":

                        return Division(number1, number2);

                    default:

                        return 0;

                }

            }

​

        }

        static void Main(string[] args)

        {

            while (true)

            {

                double firstNumber = Calculations.InsertNum();

​

                while (true)

                {

                    string getMath = Calculations.InsertMath();

                    if (getMath == "c")

                    {

                        break;

                    }

                    if (getMath == "q")

                    {

                        return;

                    }

                    double secondNumber = Calculations.InsertNum();

                    while (secondNumber == 0 && getMath == "/")

                    {

                        Console.WriteLine("Unable to divide by zero. ");

                        secondNumber = Calculations.InsertNum();

                    }

                    double result = Calculations.GetResult(firstNumber, secondNumber, getMath);

                    Console.WriteLine($"Result of operation: {firstNumber} {getMath} {secondNumber} = {result}");

                    firstNumber = result;

                }

            }

        }

    }

}

​