using System;

public class Program

{

    public static string Verification_Method()

    {   

        string userInput = Console.ReadLine();

        if ( userInput.Length != 1 || Char.IsLetter(userInput[0]) == false )

        {

            Console.WriteLine("ERROR: Invalid Input -- You entered \"" + userInput + "\"" + Environment.NewLine);

            Verification_Method();

        }   

        return userInput;

    }

    public static void CalculatePi()

    {

        Random random = new Random();

        int totalPoints = 1000000; // Total number of random points to generate

        int insideCircle = 0; // Count of points that fall inside the unit circle

​

        for (int i = 0; i < totalPoints; i++)

        {

            double x = random.NextDouble(); // Random number between 0 and 1

            double y = random.NextDouble(); // Random number between 0 and 1

​

            // Calculate the distance from the origin (0,0)

            double distance = Math.Sqrt(x * x + y * y);

​

            // If the point falls inside the unit circle, increment the counter

            if (distance <= 1)

            {

                insideCircle++;

            }

        }

​

        // Calculate an approximation of π using the Monte Carlo method

        double estimatedPi = 4.0 * insideCircle / totalPoints;

​

        Console.WriteLine("Approximation of π: " + estimatedPi);

​

        return;

    }

    public static void DrawBox()

    {

        bool widthVerification = false;

        bool heightVerification = false;

        int Width = 0;

        int Height = 0;

        while ( !widthVerification || !heightVerification )

        {

            Console.WriteLine("Enter Width: ");

            string userWidthInput = Console.ReadLine();

            if ( int.TryParse(userWidthInput, out Width) )

                {

                    widthVerification = true;

                }

            Console.WriteLine("Enter Height: ");

            string userHeightInput = Console.ReadLine();

            if ( int.TryParse(userHeightInput, out Height) )

                {

                    heightVerification = true;

                }       

            Console.WriteLine($"{Width},{Height}");

        }

        for ( int i = 0; i < Height;  i++ )

        {

            for ( int k = 0; k < Width; k++)

            {

                Console.Write("X ");

            }

            Console.WriteLine();

        }

        return;

    }

    public static void Main()

    {

        Console.WriteLine("     --- Functions! ---");

        string options = "Press A:         Calculate Pi" + Environment.NewLine +

                         "Press B:   Binomial Functions" + Environment.NewLine +

                         "Press C:          Number Sort" + Environment.NewLine +

                         "Press D:           Draw a Box";

        Console.WriteLine(options);

        string userInput = string.Empty;

        bool verification = false;

        while ( verification == false )

        {

            userInput = Verification_Method();

            verification = true;

        }

        switch (userInput.ToUpper())

        {

            case "A":

                CalculatePi();

                break;

            case "D":

                DrawBox();

                break;

        }

​

​

    }

}