using System;

class ComplexProgram
{
    static void Main()
    {

        Console.WriteLine("Hello! Please, choose what task you want to solve and enter its number.\n");
        Console.WriteLine("1. Reverses the digits of a number\n2. Calculates the average of a sequence of integers\n"
        + "3. Solves a linear equation a * x + b = 0\n");

        TaskChoice();

    }

    private static void TaskChoice()
    {
        Console.Write("Task number: ");
        int task = int.Parse(Console.ReadLine());

        switch (task)
        {
            case 1: NumberInput();
                TaskContinue();
                break;
            case 2: SequenceLength();
                TaskContinue();
                break;
            case 3: EquationInput();
                TaskContinue();
                break;
            default: Console.WriteLine("Enter a number from 1 to 3!\n");
                TaskChoice();
                break;
        }
    }
    private static void TaskContinue()
    {
        Console.WriteLine();
        Console.WriteLine("Do you want to solve something else? (Y/N)");
        char cont = char.Parse(Console.ReadLine());
        if (cont == 'Y' || cont == 'y')
        {
            TaskChoice();
        }
        else if (cont == 'N' || cont == 'n')
        {
            Console.WriteLine("Thank you for using the program!");
        }
        else
        {
            Console.WriteLine("Please, enter a correct answer!");
            TaskContinue();
        }
    }

    private static void NumberInput()
    {
        bool pos = false;
        decimal number;
        do
        {
            Console.WriteLine("Enter a positive number!");
            number = decimal.Parse(Console.ReadLine());
            if (number > 0)
            {
                pos = true;
            }
        }
        while (!pos);

        Reverse(number);
    }
    private static void Reverse(decimal number)
    {
        string stringNumber = number.ToString();
        string[] reversedNumber = new string[stringNumber.Length];

        for (int i = stringNumber.Length - 1; i >= 0; i--)
        {
            reversedNumber[stringNumber.Length - i - 1] = stringNumber[i].ToString();
        }

        foreach (string digit in reversedNumber)
        {
            Console.Write(digit);
        }
        Console.WriteLine();
    }

    private static void SequenceLength()
    {
        bool nonEmpty = false;
        int number;
        do
        {
            Console.WriteLine("Enter a how many real positive numbers will calculate!");
            number = int.Parse(Console.ReadLine());
            if (number > 0)
            {
                nonEmpty = true;
            }
        }
        while (!nonEmpty);

        InputAndCalculation(number);
    }
    private static void InputAndCalculation(int number)
    {
        Console.WriteLine("Enter the numbers:");
        int sum = 0;
        for (int i = 0; i < number; i++)
        {
            sum += int.Parse(Console.ReadLine());
        }
        Console.WriteLine("Their average sum is: {0} ", (decimal)sum / number);
    }

    private static void EquationInput()
    {
        bool pos = false;
        decimal a;
        do
        {
            Console.WriteLine("Enter the first number of linear equation - a>0!");
            a = decimal.Parse(Console.ReadLine());
            if (a > 0)
            {
                pos = true;
            }
        }
        while (!pos);
        Console.WriteLine("Enter the second number of linear equation - b!");
        decimal b = decimal.Parse(Console.ReadLine());

        EquationCalculation(a, b);

    }
    private static void EquationCalculation(decimal a, decimal b)
    {
        decimal x = 0;
        if (b > 0)
        {
            Console.WriteLine();
            Console.Write("Your linear equation is: {0}*X + {1} = 0\n", a, b);
            Console.WriteLine("X = {0}", x = -b / a);
        }
        else
        {
            Console.WriteLine();
            Console.Write("Your linear equation is: {0}*X - {1} = 0\n", a, Math.Abs(b));
            Console.WriteLine("X = {0}", x = b / a);
        }
    }
}