diff --git a/ch13/README.md b/ch13/README.md
index 889d5956..640a37de 100644
--- a/ch13/README.md
+++ b/ch13/README.md
@@ -181,3 +181,7 @@ Copy constructor and copy-assignment operator should dynamicly allocate memory f
 `StrBlob` is using smart pointers which can be managed with synthesized destructor, If an object of `StrBlob` is out of scope, the destructor for std::shared_ptr will be called automaticaly to free the memory dynamically allocated when the `use_count` goes to 0.
 
 ## Exercise 13.26 [hpp](ex13_26.h) | [cpp](ex13_26.cpp)
+
+## [Exercise 13.27](ex13_27.h)
+
+## Exercise 13.28 [hpp](ex13_28.h) | [cpp](ex13_28.cpp)
diff --git a/ch13/ex13.27.cpp b/ch13/ex13.27.cpp
deleted file mode 100644
index 378cfba1..00000000
--- a/ch13/ex13.27.cpp
+++ /dev/null
@@ -1,81 +0,0 @@
-/***************************************************************************
- *  @file       main.cpp
- *  @author     Alan.W
- *  @date       01  JAN 2014
- *  @remark
- ***************************************************************************/
-//!
-//! Exercise 13.27:
-//! Define your own reference-counted version of HasPtr.
-//!
-
-#include <string>
-#include <iostream>
-
-
-
-//! for ex13.27
-class HasPtr
-{
-public:
-    //! default constructor.
-    HasPtr(const std::string &s = std::string()):
-        ps(new std::string(s)), i(0), useCounter(new std::size_t(1)) { }
-
-    //! copy constructor.
-    HasPtr(const HasPtr& rhs) : ps(rhs.ps), i(rhs.i), useCounter(rhs.useCounter)
-    {
-        ++*useCounter;
-    }
-
-
-    HasPtr&
-    operator = (const HasPtr& rhs);
-
-
-    ~HasPtr()
-    {
-        if(--*useCounter == 0)
-        {
-            delete ps;
-            delete useCounter;
-        }
-    }
-
-private:
-    std::string* ps;
-    int    i;
-    std::size_t* useCounter;
-};
-
-
-
-int main()
-{
-    HasPtr hp("aaaaaa"), hp2;
-    HasPtr hp1(hp);
-
-    hp2 = hp1;
-
-    return 0;
-}
-
-
-inline HasPtr&
-HasPtr::operator =(const HasPtr &rhs)
-{
-    ++*rhs.useCounter;
-    if(--*useCounter == 0)
-    {
-        delete  useCounter;
-        delete  ps;
-    }
-
-    ps = rhs.ps;
-    useCounter = rhs.useCounter;
-    i = rhs.i;
-
-    return *this;
-
-}
-
diff --git a/ch13/ex13_27.h b/ch13/ex13_27.h
new file mode 100644
index 00000000..feb29967
--- /dev/null
+++ b/ch13/ex13_27.h
@@ -0,0 +1,42 @@
+//
+//  ex13_27.h
+//  Exercise 13.27
+//
+//  Created by pezy on 1/20/15.
+//  Copyright (c) 2015 pezy. All rights reserved.
+//
+//  Define your own reference-counted version of HasPtr. 
+
+#ifndef CP5_ex13_27_h
+#define CP5_ex13_27_h
+
+#include <string>
+
+class HasPtr {
+public:
+    HasPtr(const std::string &s = std::string()) : ps(new std::string(s)), i(0), use(new size_t(1)) { }
+    HasPtr(const HasPtr &hp) : ps(hp.ps), i(hp.i), use(hp.use) { ++*use; }
+    HasPtr& operator=(const HasPtr &rhs) {
+        ++*rhs.use;
+        if (--*use == 0) {
+            delete ps;
+            delete use;
+        }
+        ps = rhs.ps;
+        i = rhs.i;
+        use = rhs.use;
+        return *this;
+    }
+    ~HasPtr() {
+        if (--*use == 0) {
+            delete ps;
+            delete use;
+        }
+    } 
+private:
+    std::string *ps;
+    int i;
+    size_t *use;
+};
+
+#endif
diff --git a/ch13/ex13_28.cpp b/ch13/ex13_28.cpp
new file mode 100644
index 00000000..a8bef9d7
--- /dev/null
+++ b/ch13/ex13_28.cpp
@@ -0,0 +1,41 @@
+//
+//  ex13_28.cpp
+//  Exercise 13.28
+//
+//  Created by pezy on 1/20/15.
+//  Copyright (c) 2015 pezy. All rights reserved.
+//
+//  Given the following classes, implement a default constructor and the necessary copy-control members.
+
+#include "ex13_28.h"
+
+TreeNode& TreeNode::operator=(const TreeNode &rhs)
+{
+    ++*rhs.count;
+    if (--*count == 0) {
+        if (left) {
+            delete left;
+            left = nullptr;
+        }
+        if (right) {
+            delete right;
+            right = nullptr;
+        }
+
+        delete count;
+        count = nullptr;
+    }
+    value = rhs.value;
+    left = rhs.left;
+    right = rhs.right;
+    count = rhs.count;
+    return *this;
+}
+
+BinStrTree& BinStrTree::operator=(const BinStrTree &bst)
+{
+    TreeNode *new_root = new TreeNode(*bst.root);
+    delete root;
+    root = new_root;
+    return *this;
+}
diff --git a/ch13/ex13_28.h b/ch13/ex13_28.h
new file mode 100644
index 00000000..a19ad6a5
--- /dev/null
+++ b/ch13/ex13_28.h
@@ -0,0 +1,54 @@
+//
+//  ex13_28.h
+//  Exercise 13.28
+//
+//  Created by pezy on 1/20/15.
+//  Copyright (c) 2015 pezy. All rights reserved.
+//
+//  Given the following classes, implement a default constructor and the necessary copy-control members.
+
+#ifndef CP5_ex13_28_h
+#define CP5_ex13_28_h
+
+#include <string>
+using std::string;
+
+class TreeNode {
+public:
+    TreeNode() : value(string()), count(new int(1)), left(nullptr), right(nullptr) {}
+    TreeNode(const TreeNode &rhs) : value(rhs.value), count(rhs.count), left(rhs.left), right(rhs.right) { ++*count; }
+    TreeNode& operator=(const TreeNode &rhs);
+    ~TreeNode() {
+        if (--*count == 0) {
+            if (left) {
+                delete left;
+                left = nullptr;
+            }
+            if (right) {
+                delete right;
+                right = nullptr;
+            }
+            delete count;
+            count = nullptr;
+        }
+    }
+
+private:
+    std::string value;
+    int         *count;
+    TreeNode    *left;
+    TreeNode    *right;
+};
+
+class BinStrTree {
+public:
+    BinStrTree() : root(new TreeNode()) {}
+    BinStrTree(const BinStrTree &bst) : root(new TreeNode(*bst.root)) {}
+    BinStrTree& operator=(const BinStrTree &bst);
+    ~BinStrTree() { delete root; }
+
+private:
+    TreeNode *root;
+};
+
+#endif