Random

using System;

namespace ConsoleApplication1
{
    static class Program
    {
        static void Main()
        {
            int numSides = 20;

            for (int i = 0; i < 100; ++i)
            {
                Console.WriteLine(Roll(numSides));
            }
        }

        static int Roll(int numSides)
        {
            return rng.Next(1, numSides + 1);
        }

        static Random rng = new Random();
    }
}