Program1

static void Main(string[] args)
        {
            //The value returned from the topmenu method is stored in a variable called useroption
            ChooseOption();
            Console.ReadKey();
        }
static void ChooseOption()
    {
        int useroption;
        // excute while loop untill option is not 1-3
        do
        {

            useroption = topmenu();

            if (useroption == 1)
            {
                Console.Clear();
                Createname();
                //break;
            }

            if (useroption == 2)
            {
                Console.Clear();
                factorial();
                // break;
            }

            if (useroption == 3)
            {
                Console.Clear();
                Console.WriteLine("Thank you for using my program, Good bye !!!");
                //break;
            }

            //topmenu();
        }
        while (useroption != 3);
    }
static int topmenu()
{
    int option;
    string option_str;

    Console.Clear();
    Console.WriteLine("********************************************************************************");
    Console.WriteLine("********************************************************************************");
    Console.WriteLine("*********      OPTION 1 : Enter your name                              *********");
    Console.WriteLine("*********      OPTION 2 : Enter the number you want to factorise       *********");
    Console.WriteLine("*********      OPTION 3 : Quit                                         *********");
    Console.WriteLine("********************************************************************************");
    Console.WriteLine("********************************************************************************");
    option_str = Console.ReadLine();

    option = Convert.ToInt32(option_str);
    Console.Clear();

    if (option < 0 || option > 3)
    {
        Console.WriteLine("You have enter an invald option,");
        Console.WriteLine("Please chose a option between 1-3 (Please press any key to return to main menu)");
        Console.ReadLine();
        Console.Clear();
        //topmenu();
        ChooseOption();
    }
    else
    {
        Console.WriteLine("You have chosen option: " + option + " (Please press any key continue)");
    }
    Console.ReadKey();
    return option;
}
static void Createname()
{
    string firstname, surname, firstname_str, surname_str, userfullname;

    Console.Clear();
    Console.WriteLine("Please enter your first name ");
    firstname_str = Console.ReadLine();
    firstname = Convert.ToString(firstname_str);
    Console.Clear();
    Console.WriteLine("Please enter your surname name ");
    surname_str = Console.ReadLine();
    surname = Convert.ToString(surname_str);
    Console.Clear();
    userfullname = firstname + surname;

    Console.WriteLine("You have entered your name as " + firstname[0] + "." + surname);
    Console.WriteLine("(Please press any key to return to main menu)");
    Console.ReadKey();
    //topmenu();
    //ChooseOption();
    return;

}
static void factorial()
{


    string number_str;
    double factorial = 1;



    Console.WriteLine("Please enter number");
    number_str = Console.ReadLine();

    int num = Convert.ToInt32(number_str);


    // If statement is used so when the user inputs 0, INVALID is outputed

    if (num <= 0)
    {
        Console.WriteLine("You have enter an invald option");
        Console.WriteLine("Please enter number");
        number_str = Console.ReadLine();
        Console.Clear();


        num = Convert.ToInt32(number_str);
        //Console.Clear();
        //topmenu();
        //number_str = Console.ReadLine();
    }

    if (num >= 0)
    {

        while (num != 0)
        {
            for (int i = num; i >= 1; i--)
            {
                factorial = factorial * i;
                Console.Write(i + " * ");

            }


                Console.WriteLine("= "+factorial+ " which is factorial of " + number_str.ToString() );
                Console.WriteLine("(please any key to return to main menu)");
                Console.ReadKey();
                Console.Clear();
                break;
                //topmenu();
                //ChooseOption();

        }

    }

    //return;
}