C & C++ Interview Quiz Challenge: Pointers, OOP, and Templates | C/C++ language Multi choice questions and answers

C & C++ Interview Challenge: Pointers, OOP, and Templates

Test your knowledge of **C Fundamentals, Memory Management, Object-Oriented Programming (OOP), and Advanced C++ Features**. **Pass with 80% to proceed to the next difficulty level.**

Level 1: C Fundamentals & Pointers: 0/10 (0%)

Level 2: C++ OOP & Core Features: 0/10 (0%)

Level 3: Advanced C++ & Concurrency: 0/10 (0%)

Level 1: C Fundamentals & Pointers

1.1 What is the key difference between the C dynamic memory allocation functions `malloc()` and `calloc()`?

A. `malloc()` allocates on the stack; `calloc()` allocates on the heap. B. `calloc()` initializes the allocated memory to zero, while `malloc()` does not. C. `malloc()` is used for arrays; `calloc()` is for single variables.

**Correct Answer: B. `calloc()` initializes the allocated memory to zero, while `malloc()` does not.** `malloc()` allocates a block of memory and returns a pointer; `calloc()` takes the number of elements and their size, and sets memory to zero.

1.2 What is a Dangling Pointer?

A. A pointer that points to another pointer. B. A pointer that holds a NULL value. C. A pointer that points to a memory location that has been de-allocated (freed).

**Correct Answer: C. A pointer that points to a memory location that has been de-allocated (freed).** Accessing a dangling pointer leads to undefined behavior.

1.3 What is the primary purpose of the `const` keyword in C and C++?

A. To declare a variable whose value is determined at runtime. B. To define a constant that can only be accessed by the compiler. C. To prevent the modification of a variable, function parameter, or member function state.

**Correct Answer: C. To prevent the modification...**. `const` enforces read-only access, improving safety and enabling compiler optimizations.

1.4 What is the key functional difference between a C `struct` and a C `union`?

A. `struct` members are always private; `union` members are public. B. `union` members share the same memory location; `struct` members occupy separate memory locations. C. `struct` can only hold primitive types; `union` can hold complex types.

**Correct Answer: B. `union` members share the same memory location...**. The memory size of a union is the size of its largest member. The size of a struct is the sum of its members (plus padding).

1.5 Which storage class keyword restricts a variable's scope to the file it is declared in?

A. `extern` B. `static` (at global scope) C. `auto`

**Correct Answer: B. `static` (at global scope)**. A global `static` variable has file scope (internal linkage), meaning it is not visible to other files. Inside a function, `static` means it retains its value across function calls.

1.6 What does the C keyword `typedef` achieve?

A. It creates a new variable. B. It creates an alias or shorthand for an existing data type. C. It defines a macro constant for preprocessing.

**Correct Answer: B. It creates an alias or shorthand...**. `typedef` is commonly used to create simpler names for complex types like structs or function pointers.

1.7 Which operator is used to calculate the size in bytes of a data type or variable in C/C++?

A. `size_t` C. `sizeof` C. `size_of`

**Correct Answer: B. `sizeof`**. The `sizeof` operator returns the size of an object or type in bytes, useful for memory allocation and buffer sizing.

1.8 What does the `#include` directive do?

A. It links external libraries during the linking phase. B. It instructs the preprocessor to insert the content of another file into the current file. C. It declares a function prototype for another compilation unit.

**Correct Answer: B. It instructs the preprocessor to insert the content...**. This is a preprocessor directive that physically copies the contents of the header file at the point of the directive.

1.9 What is a Null Pointer?

A. A pointer that points to memory address 1. B. A pointer that is intentionally not pointing to any valid object or memory location. C. A pointer to a character array that is empty.

**Correct Answer: B. A pointer that is intentionally not pointing...**. A null pointer (often represented by `NULL` or `nullptr` in C++) is used to safely initialize a pointer or indicate a failure to point to a valid resource.

1.10 In C++, what is the difference between passing an argument by reference and passing it by pointer?

B. A reference must be initialized and cannot be made to point to another variable; a pointer can be changed and can be NULL. B. References are only used for objects; pointers are only for primitive types. C. Passing by pointer is safer than passing by reference.

**Correct Answer: A. A reference must be initialized and cannot be made to point to another variable; a pointer can be changed and can be NULL**. References are essentially aliases, providing cleaner syntax but less flexibility than pointers.

**End of C Fundamentals & Pointers. Click "Next Level" to continue.**

Level 2: C++ OOP & Core Features

2.1 What is the role of the `virtual` keyword in C++ inheritance?

A. It prevents a class from being inherited. B. It ensures a class can only be instantiated once. C. It enables Runtime Polymorphism by instructing the compiler to use the derived class method when accessed via a base class pointer/reference.

**Correct Answer: C. It enables Runtime Polymorphism...**. The `virtual` keyword creates a v-table (virtual table) lookup, allowing the program to dynamically select the correct function implementation at runtime.

2.2 Which C++ feature is used to resolve naming conflicts when functions or classes share the same name?

A. Operator Overloading B. Namespaces C. The `friend` keyword

**Correct Answer: B. Namespaces**. Namespaces group related classes and functions, preventing name collisions in large projects, especially when using third-party libraries (e.g., `std::`).

2.3 What is a Copy Constructor?

A. A function that creates a shallow copy of an object. B. A special constructor used to initialize a new object from an existing object of the same class. C. A method that creates a new class from an existing one.

**Correct Answer: B. A special constructor used to initialize a new object...**. It's crucial for performing **deep copies** when objects manage resources (like pointers to heap memory) to avoid issues like double deletion.

2.4 What are the four pillars of Object-Oriented Programming (OOP)?

A. Encapsulation, Inheritance, Polymorphism, Abstraction. B. Class, Object, Method, Variable. C. Constructor, Destructor, Virtual, Friend.

**Correct Answer: A. Encapsulation, Inheritance, Polymorphism, Abstraction.** These four concepts form the theoretical foundation of OOP languages like C++.

2.5 Which C++ Standard Template Library (STL) container is generally fastest for element insertion and deletion at any position?

A. `std::vector` B. `std::list` C. `std::array`

**Correct Answer: B. `std::list`**. `std::list` (a doubly linked list) has O(1) time complexity for insertion/deletion, while `std::vector` (a dynamic array) requires shifting elements, resulting in O(N).

2.6 What is Operator Overloading?

A. Defining two functions with the same name but different parameters. B. Redefining the function of an existing C++ operator (like +, -, *) for a user-defined class. C. Overriding a base class method in a derived class.

**Correct Answer: B. Redefining the function of an existing C++ operator...**. It allows operators to behave naturally with class objects (e.g., adding two complex number objects).

2.7 The access specifier `protected` grants access to:

A. Only the members of the same class. B. The members of the same class and all derived classes. C. Any function or class within the same source file.

**Correct Answer: B. The members of the same class and all derived classes**. `protected` is the key to controlled inheritance, allowing derived classes to access base class internals necessary for extension.

2.8 Why is it essential to declare a base class destructor as `virtual`?

A. To allow the destructor to accept parameters. B. To ensure the correct derived class destructor is called when deleting an object via a base class pointer. C. To prevent memory allocation during object destruction.

**Correct Answer: B. To ensure the correct derived class destructor is called...**. Failure to make the base class destructor virtual leads to resource leaks (the derived class portion is not cleaned up), known as **Undefined Behavior**.

2.9 What is Run-Time Type Information (RTTI)?

A. The ability to automatically serialize and deserialize objects. B. The mechanism that allows the type of an object to be determined at execution time (using `typeid` or `dynamic_cast`). C. A feature that lets a program manage its own memory allocation.

**Correct Answer: B. The mechanism that allows the type of an object to be determined...**. RTTI provides tools like `dynamic_cast` for safe casting between polymorphic types and `typeid` for type identification.

2.10 The C++ Standard Template Library (STL) consists primarily of which three components?

B. Containers, Algorithms, and Iterators. B. Classes, Objects, and Inheritance. C. Functions, Macros, and Header Files.

**Correct Answer: A. Containers, Algorithms, and Iterators**. Containers (like `vector`, `map`) store data; Algorithms (like `sort`, `find`) perform operations; Iterators connect containers and algorithms.

**End of C++ OOP & Core Features. Click "Next Level" to continue.**

Level 3: Advanced C++ & Concurrency

3.1 What is a Template in C++?

A. A mechanism to ensure all inherited classes implement certain methods. B. A facility for defining functions or classes that operate with generic types, known as **Generic Programming**. C. A design pattern used to create a single instance of a class.

**Correct Answer: B. A facility for defining functions or classes...**. Templates allow you to write code once and have it work with different data types (e.g., `std::vector` or `std::vector`).

3.2 What does RAII (Resource Acquisition Is Initialization) refer to?

A. Acquiring resources only when explicitly requested by the user. B. The process of initializing all variables to zero upon declaration. C. A technique where resource management (like freeing memory) is tied to the lifetime of an object (e.g., using Smart Pointers).

**Correct Answer: C. A technique where resource management...**. RAII is the core C++ technique for exception-safe resource management, ensuring resources are released automatically when the object goes out of scope (via the destructor).

3.3 What is a Pure Virtual Function?

A. A virtual function that can never be overridden. B. A virtual function declared by assigning 0 (`= 0`) in the base class, making the class **Abstract**. C. A virtual function that must return a pointer type.

**Correct Answer: B. A virtual function declared by assigning 0...**. A pure virtual function has no definition in the base class. Any class with a pure virtual function cannot be instantiated and is called an **Abstract Class**.

3.4 What are Smart Pointers (like `std::unique_ptr` and `std::shared_ptr`) primarily used for?

A. To create pointers that can access private members of a class. B. To manage heap memory automatically, preventing memory leaks by implementing RAII principles. C. To store complex data structures like linked lists.

**Correct Answer: B. To manage heap memory automatically...**. Smart pointers wrap raw pointers and use their destructors to safely call `delete` on the wrapped object when the smart pointer goes out of scope.

3.5 What is the purpose of the Rule of Three/Five in C++?

B. If a class requires a user-defined Destructor, Copy Constructor, or Copy Assignment Operator, it likely needs all three (or five, including move semantics). B. It defines the minimum number of threads a concurrent application must use. C. It states that an object can only have three public members.

**Correct Answer: A. If a class requires a user-defined Destructor...**. This rule applies when a class manages a raw resource (like memory or file handles) and ensures consistency across copying and destruction to prevent leaks.

3.6 What is a Lambda Expression in C++?

A. A template that generates a class dynamically. B. A way to define an anonymous, inline function object (closure) capable of capturing variables from its surrounding scope. C. A complex mathematical formula used for cryptographic hashing.

**Correct Answer: B. A way to define an anonymous, inline function...**. Lambdas (`[]() {}`) are essential for modern C++ and are frequently used with STL algorithms like `std::sort` and `std::for_each`.

3.7 What is the purpose of the `extern "C"` linkage specification?

A. It prevents the C++ compiler from mangling function names. B. It tells the C++ compiler to link the specified code using the C language's linking convention. C. It forces the function to be compiled without optimization.

**Correct Answer: B. It tells the C++ compiler to link the specified code using the C language's linking convention.** This is critical for interoperability, allowing C++ code to call functions defined in C libraries, which lack name mangling.

3.8 In C++11, what problem did Move Semantics primarily solve?

B. Optimizing performance by transferring ownership of temporary large resources instead of deep copying them. B. Preventing the compiler from making any copies of an object. C. Ensuring all members of a struct are aligned in memory.

**Correct Answer: A. Optimizing performance by transferring ownership...**. Move semantics (using rvalue references `&&` and move constructor/assignment) avoids expensive deep copies when dealing with temporary objects.

3.9 How do `std::thread` and `std::async` differ in managing concurrency?

A. `std::thread` is synchronous; `std::async` is asynchronous. B. `std::thread` manually creates a thread and requires manual joining; `std::async` returns a `std::future` and handles thread creation and joining automatically (RAII for concurrency). C. `std::async` is only for I/O operations.

**Correct Answer: B. `std::thread` manually creates a thread...**. `std::async` is generally preferred for simple concurrency tasks as it manages the thread lifecycle and result retrieval (`std::future`) much more safely and easily.

3.10 What is a Variadic Template?

A. A template that uses only built-in types (int, float, etc.). B. A template that can take a variable number of template arguments. C. A template whose type is restricted to `void`.

**Correct Answer: B. A template that can take a variable number of template arguments**. Variadic templates are a C++11 feature used to create powerful constructs like `std::tuple` and functions that accept variable arguments, replacing older C-style variadic functions.

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