C# の配列の良い例は何ですか?

using System;

class Demo {

   static void commonElements(int []one, int []two, int []three) {
      int i = 0, j = 0, k = 0;

      while (i < one.Length && j < two.Length && k < three.Length) {
         if (one[i] == two[j] && two[j] == three[k]) {
            Console.Write(one[i] + " ");
            i++;j++;k++;
         }

         else if (one[i] < two[j])
         i++;

         else if (two[j] < three[k])
         j++;

         else
         k++;
      }
   }

   public static void Main() {
      int []one = {20, 35, 57, 70};
      int []two = {9, 35, 57, 70, 92};
      int []three = {25, 35, 55, 57, 67, 70};

      Console.Write("Common elements: ");

      commonElements(one, two, three);
   }
}

using System;
using System.Collections;

namespace CollectionApplication {
   class Program {
      static void Main(string[] args) {
         ArrayList al = new ArrayList();

         al.Add(99);
         al.Add(47);
         al.Add(64);

         Console.WriteLine("Count: {0}", al.Count);

         Console.Write("List: ");
         foreach (int i in al) {
            Console.Write(i + " ");
         }

         Console.WriteLine();

         Console.ReadKey();
      }
   }
}

using System;

namespace ArrayApplication {
   class MyArray {
      static void Main(string[] args) {
   
         int[][] points = new int[][]{new int[]{10,5},new int[]{30,40}, new int[]{70,80},new int[]{ 60, 70 }};
int i, j;

         for (i = 0; i < 3; i++) {
            for (j = 0; j < 2; j++) {
               Console.WriteLine("a[{0}][{1}] = {2}", i, j, points[i][j]);
            }
         }

         // access
         int x = points[0][1];
         Console.WriteLine(x);
         Console.ReadKey();
      }
   }
}