If a class contains at least one pure virtual function, it is called as _______ class.

Question

Accepted Answer

The correct option is (2):

A class in an Object-Oriented Programming language like C++ that declares at least one **pure virtual function** is officially known as an **Abstract Class** or **Abstract Base Class (ABC)**. A pure virtual function is designated by setting its declaration equal to zero (e.g., virtual void functionName() = 0;). The fundamental consequence of having a pure virtual function is that the class cannot be directly instantiated, meaning you cannot create objects of that class type. Its sole purpose is to serve as a blueprint or an interface for its derived classes. Abstract classes force any concrete (non-abstract) derived class to provide a specific implementation for the pure virtual function(s), thus ensuring a common set of behaviors is implemented across the class hierarchy, which is essential for polymorphism.

The incorrect option is (1):

The term **Compiled** refers to the mechanism by which the program's source code is converted into machine-executable code using a compiler. This describes a property of the programming language itself—C++ is a compiled language—and not a classification for a specific type of class within the language's hierarchy. All C++ classes, whether they are abstract or not, are part of the source code that is processed during the compilation phase. Therefore, 'Compiled class' is not a technical term used to describe a class containing a pure virtual function.

The incorrect option is (3):

The term **Interpreted** describes the execution model of a program, where a separate program (an interpreter) executes instructions directly from the source code at runtime. This is the opposite of compilation. Since C++ is fundamentally a compiled language, classifying a class within C++ as 'Interpreted' is a misapplication of terminology and is irrelevant to the presence of virtual functions or the concept of abstraction.

The incorrect option is (4):

While an Abstract Class *functions* exactly as an **Interface**—defining a protocol that all derived classes must follow without providing an implementation—'Abstract Class' is the precise and correct terminology used in C++ for a class with one or more pure virtual functions. The formal 'Interface' keyword exists as a separate language construct in other OOP languages (like Java or C\#). In C++, the interface *concept* is directly implemented by creating a pure abstract class, which makes 'Abstract' the most accurate and technical answer choice.