In this chapter, you’ve learned the fundamental “twist” of C++: that you can place functions inside of structures. This new type of structure is called an abstract data type, and variables you create using this structure are called objects, or instances, of that type. Calling a member function for an object is called sending a message to that object. The primary action in object-oriented programming is sending messages to objects.

Although packaging data and functions together is a significant benefit for code organization and makes library use easier because it prevents name clashes by hiding the names, there’s a lot more you can do to make programming safer in C++. In the next chapter, you’ll learn how to protect some members of a struct so that only you can manipulate them. This establishes a clear boundary between what the user of the structure can change and what only the programmer may change.