diff --git a/section2/const.cpp b/section2/const.cpp
index 51dd9e3..7ac7f6d 100644
--- a/section2/const.cpp
+++ b/section2/const.cpp
@@ -65,8 +65,50 @@ class DemoClass final
     {
         m_mutex++;
     }
+    void foo(){}
+    void bar() const {
+        // m_value++;
+    }
+    int get_mutex() const {
+        return m_mutex;
+    }
+public:
+    DemoClass():m_value(0), m_mutex(0){}
 };
 
+// function calls of const instance
+void case3() {
+    using namespace std;
+    DemoClass demo;
+    demo.get_value();
+    demo.save_data();
+    demo.foo();
+    demo.bar();
+    cout << "demo's m_mutex: " << demo.get_mutex() << '\n';
+
+    const DemoClass demo1;
+    demo1.save_data();
+    demo1.get_value();
+    // demo.foo();
+    demo1.bar();
+    demo1.get_mutex();
+    cout << "demo1's m_mutex: " << demo1.get_mutex() << '\n';
+
+    const DemoClass &demo2 = DemoClass();
+    demo2.save_data();
+    demo2.get_value();
+    // demo2.foo();
+    demo2.bar();
+    cout << "demo2's m_mutex: " << demo2.get_mutex() << '\n';
+
+    const DemoClass* demo3 = &demo;
+    demo3->get_value();
+    demo3->save_data();
+    // demo3->foo();
+    demo3->bar();
+    cout << "demo3's m_mutex: " << demo3->get_mutex() << '\n';
+}
+
 
 constexpr
 int fib(int n)
@@ -84,6 +126,7 @@ int main()
 
     case1();
     case2();
+    case3();
 
     constexpr
     int fib5 = fib(5);