using System; namespace CS2026 { public class Stack { Entry top; public void Push(T data) { top = new Entry(top, data); } public T Pop() { if (top == null) { throw new InvalidOperationException(); } T result = top.data; top = top.next; return result; } class Entry { public Entry next; public T data; public Entry(Entry n, T d) { next = n; data = d; } } } }