TestBasedMenuTasks

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

namespace TextBaseMenuTasks
{
    class TextBaseMenuTasks
    {
        static void PrintMenu()
        {
            Console.WriteLine("+---------------------------------------------------+");
            Console.WriteLine("|1. Reverse the digits of a non negative number.    |");
            Console.WriteLine("|2. Calculate the avarage of a sequence of integers.|");
            Console.WriteLine("|3. Solve a linear equation a * x + b = 0 .         |");
            Console.WriteLine("+---------------------------------------------------+");
            Console.Write("Choose a task number: ");
        }

        static void ReadInput()
        {
            int task = int.Parse(Console.ReadLine());

            if (task <= 0 || task > 3)
            {
                Console.WriteLine("The chosen task is invalid.");
            }
            else if (task == 1)
            {
                Console.Write("Enter a non-negative number: ");
                int number = int.Parse(Console.ReadLine());

                if (number < 0)
                {
                    Console.WriteLine("The number you have entered is negative.");
                }
                else
                {
                    int reversed = ReverseDigits(number);
                    Console.WriteLine("The reversed number is: {0}", reversed);
                }
            }
            else if (task == 2)
            {
                Console.Write("Enter the length of the integer sequence: ");
                int sequenceLength = int.Parse(Console.ReadLine());

                if (sequenceLength <= 0)
                {
                    Console.WriteLine("The length you have entered is invalid.");
                }
                else
                {
                    int[] sequence = new int[sequenceLength];
                    Console.WriteLine("Enter the elements of the sequence:");

                    for (int i = 0; i < sequenceLength; ++i)
                    {
                        sequence[i] = int.Parse(Console.ReadLine());
                    }

                    int average = CalculateAverage(sequence);
                    Console.WriteLine("The average is: {0}", average);
                }
            }
            else
            {
                Console.WriteLine("Enter the coefficients of the equation:");
                Console.Write("a = ");
                double a = double.Parse(Console.ReadLine());

                Console.Write("b = ");
                double b = double.Parse(Console.ReadLine());

                if (a == 0.0)
                {
                    Console.WriteLine("The equation can't be solved because a = 0");
                }
                else
                {
                    double result = SolveEquation(a, b);
                    Console.WriteLine("The root x = {0}", result);
                }
            }
        }

        static int ReverseDigits(int number)
        {
            int reversed = 0;
            while (number > 0)
            {
                reversed = (reversed * 10) + (number % 10);
                number /= 10;
            }
            return reversed;
        }

        static int CalculateAverage(int[] sequence)
        {
            int sequenceLength = sequence.GetLength(0);
            int sum = 0;
            foreach (int x in sequence)
            {
                sum += x;
            }

            return sum / sequenceLength;
        }

        static double SolveEquation(double a, double b)
        {
            double result = -b / a;
            return result;
        }

        static void Main(string[] args)
        {
            PrintMenu();
            ReadInput();
        }
    }
}