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

namespace Math_Game
{
    class Program
    {
        static void Main(string[] args)
        {
            int difficulty;
            int num01;
            int num02;
            int eqIndex;
            double answer;
            Random numGenerator = new Random();

        Start:
            difficulty = 0;
            Console.WriteLine("For Easy type: 1");
            Console.WriteLine("For Medium type: 2");
            Console.WriteLine("For Hard type: 3");
            Console.WriteLine();
            Console.Write("Difficulty: ");

            try
            {
                difficulty = Convert.ToInt32(Console.ReadLine());
            }

            catch (FormatException)
            {
                Console.WriteLine("Invalid difficulty.");
                Console.WriteLine();
                goto Start;
            }

            if(difficulty == 1 || difficulty == 2 || difficulty == 3)
            {
                if (difficulty == 1)
                {
                    Console.WriteLine();
                    Console.WriteLine("Difficulty: Easy");
                    Console.WriteLine(">Press any button to start!<");
                    Console.ReadKey();
                    Console.WriteLine();
                    goto Switches;

                Switches:
                    num01 = numGenerator.Next(1, 11);
                    num02 = numGenerator.Next(1, 11);
                    eqIndex = numGenerator.Next(1, 5);

                    switch (eqIndex)
                    {
                        case 1:
                            Console.WriteLine("What's " + num01 + " + " + num02 + "?");
                            Console.Write("Answer: ");

                            try
                            {
                                answer = Convert.ToDouble(Console.ReadLine());
                            }

                            catch (FormatException)
                            {
                                Console.WriteLine("Invalid answer, number expected");
                                Console.WriteLine();
                                goto Switches;
                            }

                            if (answer == num01 + num02)
                            {
                                Console.WriteLine();
                                Console.WriteLine("Correct! :)");
                                System.Threading.Thread.Sleep(1000);
                                Console.WriteLine();
                                goto Switches;
                            }
                            else
                            {
                                Console.WriteLine();
                                Console.WriteLine("Incorrect! :(");
                                Console.WriteLine(">Press any button to restart!<");
                                Console.ReadKey();
                                Console.WriteLine();
                                goto Start;
                            }
                            break;

                        case 2:
                            Console.WriteLine("What's " + num01 + " - " + num02 + "?");
                            Console.Write("Answer: ");

                            try
                            {
                                answer = Convert.ToDouble(Console.ReadLine());
                            }

                            catch (FormatException)
                            {
                                Console.WriteLine("Invalid answer, number expected");
                                Console.WriteLine();
                                goto Switches;
                            }

                            if (answer == num01 - num02)
                            {
                                Console.WriteLine();
                                Console.WriteLine("Correct! :)");
                                System.Threading.Thread.Sleep(1000);
                                Console.WriteLine();
                                goto Switches;
                            }
                            else
                            {
                                Console.WriteLine();
                                Console.WriteLine("Incorrect! :(");
                                Console.WriteLine(">Press any button to restart!<");
                                Console.ReadKey();
                                Console.WriteLine();
                                goto Start;
                            }
                            break;

                        case 3:
                            Console.WriteLine("What's " + num01 + " * " + num02 + "?");
                            Console.Write("Answer: ");

                            try
                            {
                                answer = Convert.ToDouble(Console.ReadLine());
                            }

                            catch (FormatException)
                            {
                                Console.WriteLine("Invalid answer, number expected");
                                Console.WriteLine();
                                goto Switches;
                            }

                            if (answer == num01 * num02)
                            {
                                Console.WriteLine();
                                Console.WriteLine("Correct! :)");
                                System.Threading.Thread.Sleep(1000);
                                Console.WriteLine();
                                goto Switches;
                            }
                            else
                            {
                                Console.WriteLine();
                                Console.WriteLine("Incorrect! :(");
                                Console.WriteLine(">Press any button to restart!<");
                                Console.ReadKey();
                                Console.WriteLine();
                                goto Start;
                            }
                            break;

                        case 4:
                            Console.WriteLine("What's " + num01 + " / " + num02 + "?");
                            Console.Write("Answer: ");

                            try
                            {
                                answer = Convert.ToDouble(Console.ReadLine());
                            }

                            catch (FormatException)
                            {
                                Console.WriteLine("Invalid answer, number expected");
                                Console.WriteLine();
                                goto Switches;
                            }

                            if (answer == num01 / num02)
                            {
                                Console.WriteLine();
                                Console.WriteLine("Correct! :)");
                                System.Threading.Thread.Sleep(1000);
                                Console.WriteLine();
                                goto Switches;
                            }
                            else
                            {
                                Console.WriteLine();
                                Console.WriteLine("Incorrect! :(");
                                Console.WriteLine(">Press any button to restart!<");
                                Console.ReadKey();
                                Console.WriteLine();
                                goto Start;
                            }
                            break;
                    }
                }

                if (difficulty == 2)
                {
                    Console.WriteLine();
                    Console.WriteLine("Difficulty: Medium");
                    Console.WriteLine(">Press any button to start!<");
                    Console.ReadKey();
                    Console.WriteLine();
                    goto Switches;

                Switches:
                    num01 = numGenerator.Next(1, 21);
                    num02 = numGenerator.Next(1, 21);
                    eqIndex = numGenerator.Next(1, 5);

                    switch (eqIndex)
                    {
                        case 1:
                            Console.WriteLine("What's " + num01 + " + " + num02 + "?");
                            Console.Write("Answer: ");

                            try
                            {
                                answer = Convert.ToDouble(Console.ReadLine());
                            }

                            catch (FormatException)
                            {
                                Console.WriteLine("Invalid answer, number expected");
                                Console.WriteLine();
                                goto Switches;
                            }

                            if (answer == num01 + num02)
                            {
                                Console.WriteLine();
                                Console.WriteLine("Correct! :)");
                                System.Threading.Thread.Sleep(1000);
                                Console.WriteLine();
                                goto Switches;
                            }
                            else
                            {
                                Console.WriteLine();
                                Console.WriteLine("Incorrect! :(");
                                Console.WriteLine(">Press any button to restart!<");
                                Console.ReadKey();
                                Console.WriteLine();
                                goto Start;
                            }
                            break;

                        case 2:
                            Console.WriteLine("What's " + num01 + " - " + num02 + "?");
                            Console.Write("Answer: ");

                            try
                            {
                                answer = Convert.ToDouble(Console.ReadLine());
                            }

                            catch (FormatException)
                            {
                                Console.WriteLine("Invalid answer, number expected");
                                Console.WriteLine();
                                goto Switches;
                            }

                            if (answer == num01 - num02)
                            {
                                Console.WriteLine();
                                Console.WriteLine("Correct! :)");
                                System.Threading.Thread.Sleep(1000);
                                Console.WriteLine();
                                goto Switches;
                            }
                            else
                            {
                                Console.WriteLine();
                                Console.WriteLine("Incorrect! :(");
                                Console.WriteLine(">Press any button to restart!<");
                                Console.ReadKey();
                                Console.WriteLine();
                                goto Start;
                            }
                            break;

                        case 3:
                            Console.WriteLine("What's " + num01 + " * " + num02 + "?");
                            Console.Write("Answer: ");

                            try
                            {
                                answer = Convert.ToDouble(Console.ReadLine());
                            }

                            catch (FormatException)
                            {
                                Console.WriteLine("Invalid answer, number expected");
                                Console.WriteLine();
                                goto Switches;
                            }

                            if (answer == num01 * num02)
                            {
                                Console.WriteLine();
                                Console.WriteLine("Correct! :)");
                                System.Threading.Thread.Sleep(1000);
                                Console.WriteLine();
                                goto Switches;
                            }
                            else
                            {
                                Console.WriteLine();
                                Console.WriteLine("Incorrect! :(");
                                Console.WriteLine(">Press any button to restart!<");
                                Console.ReadKey();
                                Console.WriteLine();
                                goto Start;
                            }
                            break;

                        case 4:
                            Console.WriteLine("What's " + num01 + " / " + num02 + "?");
                            Console.Write("Answer: ");

                            try
                            {
                                answer = Convert.ToDouble(Console.ReadLine());
                            }

                            catch (FormatException)
                            {
                                Console.WriteLine("Invalid answer, number expected");
                                Console.WriteLine();
                                goto Switches;
                            }

                            if (answer == num01 / num02)
                            {
                                Console.WriteLine();
                                Console.WriteLine("Correct! :)");
                                System.Threading.Thread.Sleep(1000);
                                Console.WriteLine();
                                goto Switches;
                            }
                            else
                            {
                                Console.WriteLine();
                                Console.WriteLine("Incorrect! :(");
                                Console.WriteLine(">Press any button to restart!<");
                                Console.ReadKey();
                                Console.WriteLine();
                                goto Start;
                            }
                            break;
                    }
                }

                if (difficulty == 3)
                {
                    Console.WriteLine();
                    Console.WriteLine("Difficulty: Hard");
                    Console.WriteLine(">Press any button to start!<");
                    Console.ReadKey();
                    Console.WriteLine();
                    goto Switches;

                Switches:
                    num01 = numGenerator.Next(1, 51);
                    num02 = numGenerator.Next(1, 51);
                    eqIndex = numGenerator.Next(1, 5);

                    switch (eqIndex)
                    {
                        case 1:
                            Console.WriteLine("What's " + num01 + " + " + num02 + "?");
                            Console.Write("Answer: ");

                            try
                            {
                                answer = Convert.ToDouble(Console.ReadLine());
                            }

                            catch (FormatException)
                            {
                                Console.WriteLine("Invalid answer, number expected");
                                Console.WriteLine();
                                goto Switches;
                            }

                            if (answer == num01 + num02)
                            {
                                Console.WriteLine();
                                Console.WriteLine("Correct! :)");
                                System.Threading.Thread.Sleep(1000);
                                Console.WriteLine();
                                goto Switches;
                            }
                            else
                            {
                                Console.WriteLine();
                                Console.WriteLine("Incorrect! :(");
                                Console.WriteLine(">Press any button to restart!<");
                                Console.ReadKey();
                                Console.WriteLine();
                                goto Start;
                            }
                            break;

                        case 2:
                            Console.WriteLine("What's " + num01 + " - " + num02 + "?");
                            Console.Write("Answer: ");

                            try
                            {
                                answer = Convert.ToDouble(Console.ReadLine());
                            }

                            catch (FormatException)
                            {
                                Console.WriteLine("Invalid answer, number expected");
                                Console.WriteLine();
                                goto Switches;
                            }

                            if (answer == num01 - num02)
                            {
                                Console.WriteLine();
                                Console.WriteLine("Correct! :)");
                                System.Threading.Thread.Sleep(1000);
                                Console.WriteLine();
                                goto Switches;
                            }
                            else
                            {
                                Console.WriteLine();
                                Console.WriteLine("Incorrect! :(");
                                Console.WriteLine(">Press any button to restart!<");
                                Console.ReadKey();
                                Console.WriteLine();
                                goto Start;
                            }
                            break;

                        case 3:
                            Console.WriteLine("What's " + num01 + " * " + num02 + "?");
                            Console.Write("Answer: ");

                            try
                            {
                                answer = Convert.ToDouble(Console.ReadLine());
                            }

                            catch (FormatException)
                            {
                                Console.WriteLine("Invalid answer, number expected");
                                Console.WriteLine();
                                goto Switches;
                            }

                            if (answer == num01 * num02)
                            {
                                Console.WriteLine();
                                Console.WriteLine("Correct! :)");
                                System.Threading.Thread.Sleep(1000);
                                Console.WriteLine();
                                goto Switches;
                            }
                            else
                            {
                                Console.WriteLine();
                                Console.WriteLine("Incorrect! :(");
                                Console.WriteLine(">Press any button to restart!<");
                                Console.ReadKey();
                                Console.WriteLine();
                                goto Start;
                            }
                            break;

                        case 4:
                            Console.WriteLine("What's " + num01 + " / " + num02 + "?");
                            Console.Write("Answer: ");

                            try
                            {
                                answer = Convert.ToDouble(Console.ReadLine());
                            }

                            catch (FormatException)
                            {
                                Console.WriteLine("Invalid answer, number expected");
                                Console.WriteLine();
                                goto Switches;
                            }

                            if (answer == num01 / num02)
                            {
                                Console.WriteLine();
                                Console.WriteLine("Correct! :)");
                                System.Threading.Thread.Sleep(1000);
                                Console.WriteLine();
                                goto Switches;
                            }
                            else
                            {
                                Console.WriteLine();
                                Console.WriteLine("Incorrect! :(");
                                Console.WriteLine(">Press any button to restart!<");
                                Console.ReadKey();
                                Console.WriteLine();
                                goto Start;
                            }
                            break;
                    }
                }
            } else
            {
                Console.WriteLine("Invalid difficulty.");
                Console.WriteLine();
                goto Start;
            }
            Console.ReadKey();
        }
    }
}