MergeSort

using System;

namespace _13MergeSort
{
    class MergeSort
    {
        static void Main()
        {
            int length;
            bool correct;
            do
            {
                Console.WriteLine("Please input the length of the array");
                correct = int.TryParse(Console.ReadLine(), out length) && length > 0;
                if (!correct)
                {
                    Console.WriteLine("This is not a correct number!");
                }
            } while (!correct);
            int[] array = new int[length];
            Console.WriteLine("Please input the integer numbers of the array.");
            for (int i = 0; i < length; i++)
            {
                array[i] = int.Parse(Console.ReadLine());
            }
            Console.WriteLine("The array is:");
            Console.WriteLine(String.Join(", ", array));
            array = Sort(array);
            Console.WriteLine("The sorted array is:");
            Console.WriteLine(String.Join(", ", array));
        }

        static int[] Sort(int[] array)
        {
            if (array.Length < 2)
            {
                return array;
            }
            int middle = array.Length / 2;
            int[] left = new int[middle];
            for (int i = 0; i < left.Length; i++)
            {
                left[i] = array[i];
            }
            int[] right = new int[array.Length - middle];
            for (int i = 0; i < right.Length; i++)
            {
                right[i] = array[middle + i];
            }

            Sort(left);
            Sort(right);

            int leftIndex = 0;
            int rightIndex = 0;
            for (int i = 0; i < array.Length; i++)
            {
                if (leftIndex < left.Length && rightIndex < right.Length)
                {
                    if (left[leftIndex] <= right[rightIndex])
                    {
                        array[i] = left[leftIndex];
                        leftIndex++;
                    }
                    else
                    {
                        array[i] = right[rightIndex];
                        rightIndex++;
                    }
                }
                else if (leftIndex == left.Length)
                {
                    array[i] = right[rightIndex];
                    rightIndex++;
                }
                else
                {
                    array[i] = left[leftIndex];
                    leftIndex++;
                }
            }
            return array;
        }
    }
}