Marie-Cécile Auzeill:

using System;
using System.Collections.Generic;
using System.Text;
using System.Threading;
namespace noel
{
 class Program
 {
  static void Main(string[] args)
  {
   System.Random nRandomPosition =
      new System.Random();
   while (true)
   {
    char[] tab = new char[80];
    tab[nRandomPosition.Next(0, 79)] = '.';
    System.Console.WriteLine(tab);
    System.Threading.Thread.Sleep(100);
   }
  }
 }
}