restructure and add ipi texs

ws2019/ipi/uebungen/cpp_headers/UseStack.cc

@@ -0,0 +1,20 @@
+#include<cassert>
+#include<iostream>
+
+#include"DLL.hh"
+#include"Stack.hh"
+
+int main ()
+{
+  Stack<int> s1;
+  for (int i=1; i<=5; i++)
+    s1.push(i);
+    
+  Stack<int> s2(s1);
+  s2 = s1;
+  while (!s2.empty())
+    {
+      std::cout << s2.top() << std::endl;
+      s2.pop();
+    }
+}