C# のスタック クラスでのプッシュとポップ

Stack st = new Stack();

st.Push('A');
st.Push('B');
st.Push('C');
st.Push('D');

Using System;
using System.Collections;

namespace CollectionsApplication {
   class Program {
      static void Main(string[] args) {
         Stack st = new Stack();

         st.Push('A');
         st.Push('B');
         st.Push('C');
         st.Push('D');

         Console.WriteLine("Current stack: ");
         foreach (char c in st) {
            Console.Write(c + " ");
         }
         Console.WriteLine();

         st.Push('P');
         st.Push('Q');
         Console.WriteLine("The next poppable value in stack: {0}", st.Peek());
         Console.WriteLine("Current stack: ");

         foreach (char c in st) {
            Console.Write(c + " ");
         }

         Console.WriteLine();
         Console.WriteLine("Removing values....");
         st.Pop();
         st.Pop();
         st.Pop();
         Console.WriteLine("Current stack: ");
         foreach (char c in st) {
            Console.Write(c + " ");
         }
      }
   }
}