adding unique ptr example

lectures/27_garbage_collection/README.md

@@ -380,3 +380,31 @@ int main(){
         return 0;
 }
 ```
+
+## 27.16 Exercise
+
+Read the following [program](unique_ptr1.cpp) and answer the questions.
+
+```cpp
+#include <iostream>
+#include <memory>
+
+int main(){
+        // Question: is this valid or invalid syntax?
+        // std::unique_ptr<std::string> s1("test1");
+
+        std::unique_ptr<std::string> s1(new std::string("test1"));
+
+        std::cout << *s1 << std::endl;
+        // Question: can we do this: std::cout << s1.size() << std::endl;
+        std::cout << s1->size() << std::endl;
+
+        std::unique_ptr<std::string> s2(std::move(s1));
+
+        // Question: which of the following line will trigger a seg fault?
+        // std::cout << "s1:" << *s1 << std::endl;
+        // std::cout << "s2:" << *s2 << std::endl;
+
+        return 0;
+}
+```

lectures/27_garbage_collection/unique_ptr1.cpp

@@ -0,0 +1,21 @@
+#include <iostream>
+#include <memory>
+
+int main(){
+	// Question: is this valid or invalid syntax?
+	// std::unique_ptr<std::string> s1("test1");
+	
+	std::unique_ptr<std::string> s1(new std::string("test1"));
+
+	std::cout << *s1 << std::endl;
+	// Question: can we do this: std::cout << s1.size() << std::endl;
+	std::cout << s1->size() << std::endl;
+
+	std::unique_ptr<std::string> s2(std::move(s1));
+
+	// Question: which of the following line will trigger a seg fault?
+	// std::cout << "s1:" << *s1 << std::endl;
+	// std::cout << "s2:" << *s2 << std::endl;
+
+	return 0;
+}