FillTheMatrix

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

namespace ConsoleApplication7
{
    class Program
    {

        static void Main(string[] args)
        {
            int size = int.Parse(Console.ReadLine());
            int[,] matrix = new int[size, size];
            int rows = matrix.GetLength(1);
            int cols = matrix.GetLength(0);
            int counterOutput = 1;
            for (int i = 0; i < rows; i++)
            {
                if (i % 2 == 0)
                {
                    for (int j = 0; j < cols; j++)
                {
                    matrix[j , i] = counterOutput;
                    counterOutput++;
                }
                }
                else
                {
                    for (int j = cols - 1; j >= 0; j--)
                    {
                        matrix[j, i] = counterOutput;
                        counterOutput++;
                    }
                }
            }

            Console.WriteLine("The matrix is as follows:");
            for (int row = 0; row < matrix.GetLength(0); row++)
            {
                for (int col = 0; col < matrix.GetLength(1); col++)
                {
                    Console.Write("{0} ", matrix[row, col]);
                }

                Console.WriteLine();
            }
        }
    }
}