diff --git a/Trenser.VehicleServiceSystem/Trenser.VehicleServiceSystem/controllers/Controller.cpp b/Trenser.VehicleServiceSystem/Trenser.VehicleServiceSystem/controllers/Controller.cpp
index 31f0129..ddf5354 100644
--- a/Trenser.VehicleServiceSystem/Trenser.VehicleServiceSystem/controllers/Controller.cpp
+++ b/Trenser.VehicleServiceSystem/Trenser.VehicleServiceSystem/controllers/Controller.cpp
@@ -1 +1,139 @@
 #include "Controller.h"
+
+bool Controller::login(const std::string& username, const std::string& password)
+{
+    return false;
+}
+
+void Controller::logout()
+{
+}
+
+void Controller::changePassword(const std::string& newPassword)
+{
+}
+
+void Controller::createCustomer(const std::string& username, const std::string& password, const std::string& email, const std::string& phone)
+{
+}
+
+const User* Controller::getAuthenticatedUser()
+{
+    return nullptr;
+}
+
+void Controller::createTechnician(const std::string& username, const std::string& password, const std::string& email, const std::string& phone)
+{
+}
+
+void Controller::updateUserDetails(const std::string& email, const std::string& phone)
+{
+}
+
+util::Map<std::string, const Service*> Controller::getServices()
+{
+}
+
+util::Map<std::string, const ComboPackage*> Controller::getComboPackages()
+{
+}
+
+void Controller::purchaseService(const util::Vector<std::string>& serviceIDs, const std::string& vehicleNumber, const std::string& vehicleBrand, const std::string& vehicleModel)
+{
+}
+
+void Controller::purchaseComboPackage(const std::string& comboPackageID, const std::string& vehicleNumber, const std::string& vehicleBrand, const std::string& vehicleModel)
+{
+}
+
+util::Map<std::string, const InventoryItem*> Controller::getInventoryItems()
+{
+}
+
+const InventoryItem* Controller::getInventoryItem(const std::string& inventoryItemID)
+{
+    return nullptr;
+}
+
+void Controller::addInventoryItem(const std::string& partName, int quantity, double price)
+{
+}
+
+void Controller::removeInventoryItem(const std::string& inventoryItemID)
+{
+}
+
+util::Map<std::string, const ServiceBooking*> Controller::getServiceBookings()
+{
+}
+
+util::Map<std::string, const ServiceBooking*> Controller::getServiceBookingsByUser(const std::string userID)
+{
+}
+
+util::Map<std::string, const User*> Controller::getUsers()
+{
+}
+
+util::Map<std::string, const User*> Controller::getUsers(util::UserType userType)
+{
+}
+
+void Controller::createJobCard(const std::string& bookingID, const std::string& technicianID, const std::string& serviceID)
+{
+}
+
+void Controller::createService(const std::string& name, const util::Vector<std::string>& inventoryItemIDs, double laborCost)
+{
+}
+
+void Controller::removeService(const std::string& serviceID)
+{
+}
+
+util::Map<std::string, const JobCard*> Controller::getJobCardsByUser()
+{
+    return util::Map<std::string, const JobCard*>();
+}
+
+void Controller::completeJob(const std::string& jobID)
+{
+}
+
+void Controller::removeUser(const std::string& userID)
+{
+}
+
+void Controller::createComboPackage(const std::string& name, const util::Vector<std::string>& serviceIDs, double discountPercentage)
+{
+}
+
+void Controller::removeComboPackage(const std::string& comboPackageID)
+{
+}
+
+util::Map<std::string, const Invoice*> Controller::getInvoicesByUser()
+{
+    return util::Map<std::string, const Invoice*>();
+}
+
+void Controller::completePayment(const std::string& invoiceID, util::PaymentMode paymentMode)
+{
+}
+
+util::Vector<const Notification*> Controller::getNotifications()
+{
+}
+
+void Controller::deleteNotification(const std::string& notificationID)
+{
+}
+
+void Controller::configureNotifications(const std::string& userID, bool paymentNotifications, bool serviceNotifications)
+{
+}
+
+void Controller::runSystemChecks()
+{
+}
+
diff --git a/Trenser.VehicleServiceSystem/Trenser.VehicleServiceSystem/controllers/Controller.h b/Trenser.VehicleServiceSystem/Trenser.VehicleServiceSystem/controllers/Controller.h
index 638b751..3aabb58 100644
--- a/Trenser.VehicleServiceSystem/Trenser.VehicleServiceSystem/controllers/Controller.h
+++ b/Trenser.VehicleServiceSystem/Trenser.VehicleServiceSystem/controllers/Controller.h
@@ -19,32 +19,32 @@ public:
     void logout();
     void changePassword(const std::string& newPassword);
     void createCustomer(const std::string& username, const std::string& password, const std::string& email, const std::string& phone);
-    User* const getAuthenticatedUser();
+    const User* getAuthenticatedUser();
     void createTechnician(const std::string& username, const std::string& password, const std::string& email, const std::string& phone);
     void updateUserDetails(const std::string& email, const std::string& phone);
-    util::Map<std::string, Service*> getServices();
-    util::Map<std::string, ComboPackage*> getComboPackages();
+    util::Map<std::string, const Service*> getServices();
+    util::Map<std::string, const ComboPackage*> getComboPackages();
     void purchaseService(const util::Vector<std::string>& serviceIDs, const std::string& vehicleNumber, const std::string& vehicleBrand, const std::string& vehicleModel);
     void purchaseComboPackage(const std::string& comboPackageID, const std::string& vehicleNumber, const std::string& vehicleBrand, const std::string& vehicleModel);
-    util::Map<std::string, InventoryItem*> getInventoryItems();
-    InventoryItem* getInventoryItem(const std::string& inventoryItemID);
+    util::Map<std::string, const InventoryItem*> getInventoryItems();
+    const InventoryItem* getInventoryItem(const std::string& inventoryItemID);
     void addInventoryItem(const std::string& partName, int quantity, double price);
     void removeInventoryItem(const std::string& inventoryItemID);
-    util::Map<std::string, ServiceBooking*> getServiceBookings();
-    util::Map<std::string, ServiceBooking*> getServiceBookingsByUser();
-    util::Map<std::string, User*> getUsers();
-    util::Map<std::string, User*> getUsers(util::UserType type);
+    util::Map<std::string, const ServiceBooking*> getServiceBookings();
+    util::Map<std::string, const ServiceBooking*> getServiceBookingsByUser(const std::string userID);
+    util::Map<std::string, const User*> getUsers();
+    util::Map<std::string, const User*> getUsers(util::UserType userType);
     void createJobCard(const std::string& bookingID, const std::string& technicianID, const std::string& serviceID);
     void createService(const std::string& name, const util::Vector<std::string>& inventoryItemIDs, double laborCost);
     void removeService(const std::string& serviceID);
-    util::Map<std::string, JobCard*> getJobCardsByUser();
+    util::Map<std::string, const JobCard*> getJobCardsByUser();
     void completeJob(const std::string& jobID);
     void removeUser(const std::string& userID);
     void createComboPackage(const std::string& name, const util::Vector<std::string>& serviceIDs, double discountPercentage);
     void removeComboPackage(const std::string& comboPackageID);
-    util::Map<std::string, Invoice*> getInvoicesByUser();
+    util::Map<std::string, const Invoice*> getInvoicesByUser();
     void completePayment(const std::string& invoiceID, util::PaymentMode paymentMode);
-    util::Vector<Notification*> getNotifications();
+    util::Vector<const Notification*> getNotifications();
     void deleteNotification(const std::string& notificationID);
     void configureNotifications(const std::string& userID, bool paymentNotifications, bool serviceNotifications);
     void runSystemChecks();
diff --git a/Trenser.VehicleServiceSystem/Trenser.VehicleServiceSystem/views/UserInterface.cpp b/Trenser.VehicleServiceSystem/Trenser.VehicleServiceSystem/views/UserInterface.cpp
index 48c17e5..122f9a8 100644
--- a/Trenser.VehicleServiceSystem/Trenser.VehicleServiceSystem/views/UserInterface.cpp
+++ b/Trenser.VehicleServiceSystem/Trenser.VehicleServiceSystem/views/UserInterface.cpp
@@ -2,7 +2,7 @@
 #include "InputHelper.h"
 #include "OutputHelper.h"
 
-void UserInterface::run() const
+void UserInterface::run()
 {
 	bool isMenuActive = true;
 	while (isMenuActive)
@@ -26,7 +26,7 @@ void UserInterface::run() const
 	}
 }
 
-bool UserInterface::handleOperation(int choice) const
+bool UserInterface::handleOperation(int choice)
 {
 	switch (choice)
 	{
@@ -46,12 +46,12 @@ bool UserInterface::handleOperation(int choice) const
 	return true;
 }
 
-void UserInterface::login() const
+void UserInterface::login()
 {
 
 }
 
-void UserInterface::registerCustomer() const
+void UserInterface::registerCustomer()
 {
 
 }
diff --git a/Trenser.VehicleServiceSystem/Trenser.VehicleServiceSystem/views/UserInterface.h b/Trenser.VehicleServiceSystem/Trenser.VehicleServiceSystem/views/UserInterface.h
index d7fc250..da3862e 100644
--- a/Trenser.VehicleServiceSystem/Trenser.VehicleServiceSystem/views/UserInterface.h
+++ b/Trenser.VehicleServiceSystem/Trenser.VehicleServiceSystem/views/UserInterface.h
@@ -11,10 +11,10 @@ private:
     AdminMenu m_adminMenu;
     TechnicianMenu m_technicianMenu;
     CustomerMenu m_customerMenu;
-    bool handleOperation(int choice) const;
+    bool handleOperation(int choice);
 public:
     UserInterface() {}
-    void run() const;
-    void login() const;
-    void registerCustomer() const;
+    void run();
+    void login();
+    void registerCustomer();
 };