using System;

​

public class Program

{

    public static void Main()

    {

        int nbrOfDigit = 1;

        double price = Math.Round(4.0, nbrOfDigit);

        string nbrStr = Math.Round(price, nbrOfDigit).ToString("0." + ReplicateString('0', nbrOfDigit));

        Console.WriteLine(nbrStr);

        string lastStr = nbrStr.Substring(nbrStr.Length - 1);

        Console.WriteLine(lastStr);

        string value = "0." + ReplicateString('0', nbrOfDigit-1) + 9;

        double convertedValue = Convert.ToDouble(value);

        Console.WriteLine(price + convertedValue);

        Console.WriteLine(Math.Round(4.88, 1));

    }

​

    public static string ReplicateString(char Source, int Times)

    {

        if (Times < 1)

        {

            return "";

        }

        else

        {

            return new string (Source, Times);

        }

    }

}