using System;
using System.Collections.Generic;
using System.Text;

namespace brute1
{
    class Program
    {
        public char[] mass ={'a','b','c','d' };
        static void Main(string[] args)
        {
            Program pr = new Program();
            for (int i = 0; i<pr.mass.Length; i++)
            {
                for (int j = 0; j <pr.mass.Length; j++)
                {
                    Console.WriteLine("->" + pr.mass[i] + pr.mass[j]);
                }
            }
            Console.ReadLine();
        }
    }
}

...
Dictionary<int, string> myDict = new Dictionary<int, string>();
...
myDict.add(1,"Первый");
myDict.add(2,"Второй");
...
myDict.add(100,"Сотый");
...

Console.WriteLine(myDict[3]);