CS401 is a coursebook offered by Virtual University of Pakistan as part of the Bachelor of Science in Computer Science degree program. The book covers various topics related to object-oriented programming in C++, including classes and objects, inheritance, polymorphism, templates, and the Standard Template Library (STL). The book begins by introducing object-oriented programming concepts, such as encapsulation and abstraction, and discusses the C++ programming language features that enable these concepts. It then delves into classes and objects, covering topics such as constructors, destructors, access modifiers, and member functions. The book also covers inheritance, a key concept in object-oriented programming, explaining how to create derived classes from base classes and how to use virtual functions to achieve runtime polymorphism. It then moves on to cover templates, which allow for the creation of generic functions and classes that can be used with different data types. Finally, the book covers the Standard Template Library (STL), which provides a collection of generic algorithms, containers, and iterators that can be used to manipulate data efficiently. The book covers containers such as vectors, lists, and maps, as well as algorithms such as sorting, searching, and transforming. Throughout the book, there are numerous examples and exercises that allow students to practice and apply the concepts learned. Additionally, the book provides useful tips and best practices for programming in C++, helping students to write clean, efficient, and maintainable code. Overall, CS401 is a comprehensive guide to object-oriented programming in C++, providing students with a strong foundation in the language and its features. It is a valuable resource for anyone looking to learn or improve their skills in C++ programming.