C# is an object-oriented programming language. The four basic principles of object-oriented programming are: Abstraction Modeling the relevant attributes and interactions of entities as classes to define an abstract representation of a system.

Create a new file named BankAccount.cs in the Classes directory. This file contains the definition of a bank account. Object Oriented programming organizes code by creating types in the form of classes. These classes contain the code that represents a specific entity. The BankAccount class represents a bank account.

The goal of object-oriented programming (OOP) is to create objects that have methods and data. Abstraction is the process of keeping some details hidden and only displaying to the user the information that is absolutely necessary. Stated differently, "Abstraction focuses on what an object does instead of how it does."

This tutorial demonstrated many of the techniques used in Object-Oriented programming: You used Abstraction when you defined classes for each of the different account types. Those classes described the behavior for that type of account. You used Encapsulation when you kept many details private in each class.