In C++, what is the primary purpose of using namespaces in a program?

Introduction / Context:
Namespaces are a core feature of C++ that help manage the complexity of large programs and libraries. As code bases grow, the risk of name collisions between functions, classes, and variables from different modules increases. Namespaces provide a mechanism to group related identifiers and to control how they are made visible. This question focuses on the main motivation for using namespaces in everyday C++ development.

Given Data / Assumptions:

• The language is C++ and the feature in question is the namespace construct.
• We are considering typical use cases, not obscure corner cases.
• Encapsulation of identifiers and logical program structure are both mentioned as possible purposes.
• We assume familiarity with the standard namespace std as a real world example.

Concept / Approach:
A namespace in C++ provides a named scope for identifiers. All names defined inside the namespace are encapsulated within that namespace, which prevents conflicts with identical names defined elsewhere. At the same time, namespaces allow developers to organise code into logical units, such as grouping all library functions for a module under a single namespace name. This dual role of encapsulation and structuring is the primary reason namespaces were introduced into the language. Without namespaces, large projects would require complex naming conventions or risk frequent name clashes.

Step-by-Step Solution:
Step 1: Recall that a namespace is introduced with the keyword namespace followed by a name and a block of declarations. Step 2: Understand that everything declared inside the namespace is accessed using the scope resolution operator, such as mylib::Function. Step 3: Recognise that this mechanism encapsulates identifiers, because code outside the namespace must either qualify names or use directives so that they do not accidentally clash with other code. Step 4: Notice that namespaces also serve to group related functionality, making it easier to understand that certain classes and functions belong to the same logical module. Step 5: Conclude that both encapsulation and logical structuring are key purposes, so the best answer is the option that includes both.

Verification / Alternative check:
Consider the standard namespace std. It contains the standard library's streams, containers, algorithms, and many other components. If these names were all declared at global scope without a namespace, they would collide with user-defined identifiers far more often. The namespace groups all standard names logically together while protecting them behind the std:: qualifier. This practical example confirms that the main purpose of namespaces is both to encapsulate and to structure identifiers into coherent units.

Why Other Options Are Wrong:
Option To encapsulate data: This is partially correct, but it ignores the equally important role of providing a logical structure for modules and libraries. Option To structure a program into logical units: Also partially correct, but it does not explicitly acknowledge the role of namespaces in preventing name clashes. Option None of these: This is incorrect because both encapsulation and logical grouping are documented design goals for namespaces.

Common Pitfalls:
One pitfall is to use using namespace std in global scope in header files, which can pollute the global namespace and defeat some benefits of namespaces. Another mistake is to create many small namespaces without clear structure, which can make code harder to navigate. A disciplined use of namespaces, where each namespace meaningfully groups related code and limits name collisions, leads to cleaner and more maintainable C++ projects.

Final Answer:
The primary purpose of namespaces is Both a and b (encapsulation and logical grouping), that is, to encapsulate data and to structure a program into logical units.