C and C++ Interview Questions and Answers

Introduction

C and C++ are popular programming languages used in the software industry. C is great because it is very fast and can work directly with computer hardware. This makes it perfect for things like operating systems and other low-level programming tasks. C++ is basically a version of C that adds useful features like object-oriented programming. This helps people make complicated programs that are easy to understand and reuse. People use C and C++ widely in areas like game development, desktop applications, and real-time systems. In this guide, you will learn about the C and C++ interview questions and answers, including the questions that people usually ask in interviews and simple explanations that are easy to understand, even if you are just starting with C and C++. Discover our C and C++ Course Syllabus to start your programming journey.

C and C++ Interview Questions for Freshers

1. What are the main features of C?

C is a programming language. Below are the main features of C:

• Structured and procedural programming.
• Portable and machine-independent language.
• Fast. Efficient performance.
• Supports pointers for direct memory access.
• Collection of built-in functions.
• Easy to build modular programs using functions.

These features make C suitable for operating systems, embedded systems, and software applications.

2. What is a Pointer?

A pointer is a variable. It stores the memory address of another variable. Pointers are mainly used for dynamic memory allocation, arrays, and function handling in C and C++.

3. What is the difference between malloc() and calloc()?

Both malloc() and calloc() are memory allocation functions in C. They work differently.

• malloc() allocates a block of memory. 
• The allocated memory contains garbage values.
• calloc() allocates memory blocks. 
• The allocated memory is automatically initialized to zero.

These functions are commonly used in dynamic memory management.

4. What is the difference between a struct and a union?

A struct and a union are user-defined data types in C. They store data differently.

• In a struct, each member gets memory space.
• In a union, all members share the memory location.
• A union saves memory because it uses the size of the largest member only.

Structures are mainly used when all values need to be stored, like in a database.

5. Explain the static keyword.

The static keyword is used to keep the value of a variable. It helps to retain the value between function calls. A static variable is initialized once during the program execution.

Some important points about variables:

• Retains value between function calls.
• Initialized once.
• The default value is 0 if not initialized.
• Memory is allocated permanently during program execution.

6. What is a preprocessor directive?

Preprocessor directives are instructions processed before the actual compilation starts. These directives start with the # symbol.

Common examples include:

• #include → Used to include header files.
• #define → Used in programming to define reusable constants or macros.
• #ifdef → Used for conditional compilation.

Preprocessor directives help make the code simpler and more organized.

7. What is the difference between ++i and i++?

Both operators are used to increment a value by 1. The order of execution is different.

• +i (Prefix Increment). 
  • First increases the value. 
  • Then uses the updated value.
• i++ (Postfix Increment). 
  • First uses the value. 
  • Then increases the value.

This difference becomes important in expressions and loops.

8. What is the difference between C and C++?

C and C++ are both programming languages. They follow different approaches.

• C
  • C is a programming language.
  • C focuses more on functions and procedures.
• C++
  • C++ supports object-oriented programming concepts.
  • C++ includes classes, inheritance, polymorphism, and abstraction.
  • C++ makes it easier to build big and complex applications.

C++ is often thought of as an extension or superset of C.

9. What are Class and Objects in C++?

In C++, a class is a blueprint. It is used to create objects. A class contains variables and functions that define the properties and behavior of an object.

An object is an instance of a class. It is created during program execution.

For example:

• Class → Car
• Object → BMW, Audi, Tesla

Classes and objects are the foundation of object-oriented programming in C++.

10. Explain the differences between struct and class.

The main difference between a struct and a class in C++ is the default access level.

• struct members are public by default.
• class members are private by default.

Apart from this, both can contain variables, functions, constructors, and other features.

11. What are a Constructor and a Destructor?

A constructor is a member function. It automatically initializes an object when it is created. A destructor is used to release resources and clean up memory when the object is destroyed.

Some points:

• A class constructor is defined using the class name.
• Constructors do not have a return type.
• Destructors are automatically called when objects go out of scope.
• Destructors help prevent memory leaks.

12. What is Polymorphism?

Polymorphism means ” forms.” It allows the function or method to behave differently. It depends on the object or situation.

Types of polymorphism in C++ include:

• Function Overloading
• Operator Overloading
• Virtual Functions

Polymorphism improves code flexibility and reusability.

13. What is a Virtual Function?

A virtual function is a function. It is declared in a base class and overridden in a class. It helps achieve runtime polymorphism in C++.

Some benefits of functions:

• Supports dynamic method overriding.
• Improves flexibility in inheritance.
• Enables runtime decision-making.

Virtual functions are a concept in object-oriented programming.

14. What is the difference between a Pointer and a Reference?

Pointers and references are both used to access variables. They work differently.

• A pointer can store NULL values. 
• A pointer can be reassigned to another address.
• A reference variable must be assigned when it is declared.
• A reference always remains linked to the same variable.

References are generally safer and easier to use than pointers.

15. What is the this pointer?

The this pointer is a keyword in C++. It points to the object calling a member function.

Main uses of the this pointer:

• Refers to the object.
• Helps avoid naming conflicts.
• Can return the object from a function.

The this pointer is automatically available, inside static member functions.

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C and C++ Interview Questions for Experienced Candidates

1. What is a Virtual Table (vtable) and Virtual Table Pointer (vptr)?

A Virtual Table, also called a vtable, is used in C++ to support runtime polymorphism. It is like a table that stores the addresses of virtual functions in a class.

Important points about Tables and Virtual Table Pointers:

• Every class that has functions has a Virtual Table.
• The Virtual Table has function pointers.
• Each object has a pointer called a Virtual Table Pointer.
• The Virtual Table Pointer points to the Virtual Table.

This helps C++ figure out which function to call when the program is running.

2. Explain RAII (Resource Acquisition Is Initialization).

RAII is a programming technique that automates resource allocation and release in C++. This means that resources are obtained in the constructor and let go in the destructor.

Resources can be things like:

• Memory
• File handles
• Database connections
• Mutex locks

Using Resource Acquisition Is Initialization helps prevent memory leaks and makes the program safer when errors happen.

3. What are the differences between smart pointers (unique_ptr, shared_ptr, weak_ptr)?

These are pointers that were added to modern C++ to make memory management safer.

• unique_ptr:
  • Owns a resource all by itself.
  • One pointer can own the object.
• shared_ptr:
  • Multiple pointers own the object.
  • Uses reference counting.
• weak_ptr:
  • Looks at a shared_ptr
  • Does not increase the reference count.
  • Helps avoid references.

Smart pointers reduce manual memory management errors.

4. Can you explain how Deep Copy differs from Shallow Copy?

• A Shallow Copy is when you copy the values of an object’s members directly, including the addresses of pointers. This means that multiple objects might point to the same place in memory.
• A Deep Copy is when you make a memory and copy the actual data, so the objects are completely independent.
• The main differences are:
  • Shallow Copy shares memory.
  • Deep Copy makes a new memory.
  • Deep Copy is safer when working with memory.

5. What is the purpose of std::move and Rvalue References?

std::move and rvalue references were introduced in C++11 to improve performance by avoiding unnecessary copying.

The main benefits are:

• It transfers resources by copying them.
• It makes the program run faster and more efficiently.
• It is useful for objects.

Rvalue References use the && symbol and support move semantics in modern C++.

6. Explain the difference between new/delete and malloc/free.

Both are used to allocate memory, but they work differently.

• new and delete are:
  • C++ operators
  • Call constructors and destructors
  • Type-safe
• malloc and free are:
  • C library functions
  • Allocate memory only
  • Do not call constructors or destructors

new and delete are usually preferred in C++ programs.

7. What are C++11/14/17 features used in modern code?

Modern C++ introduces powerful features that improve readability and performance.

Some popular features are:

• The auto keyword
• Lambda expressions
• Range-based for loops
• pointers
• nullptr
• constexpr
• Structured bindings
• Move semantics

These features make C++ coding cleaner and more efficient.

8. What is Function Overloading vs. Operator Overloading vs. Overriding?

These are concepts in object-oriented programming.

• Function Overloading:
  • When you have the function name.
  • With different parameters.
• Operator Overloading:
  • When you redefine operators for user-defined classes.
• Overriding:
  • When a derived class replaces a base class function.

These concepts make the code more flexible and reusable.

9. What is a Segmentation Fault, and what causes it?

A segmentation fault happens when a program accesses restricted or invalid memory.

Common causes are:

• Using pointers
• Accessing memory that has already been freed.
• Buffer overflow
• Stack overflow
• Using dangling pointers

Segmentation Faults usually make the program crash.

10. What is a “Dangling Pointer” and how to avoid it?

A Dangling Pointer is a pointer that points to memory that has already been deleted or freed.

Ways to avoid dangling pointers:

• Initialize pointers to NULL or nullptr
• Set pointers to NULL after freeing memory
• Use pointers whenever possible

Taking care of memory properly helps avoid unexpected program errors.

11. Explain the volatile keyword.

The volatile keyword tells the compiler that a variable’s value can change unexpectedly at any time.

It is commonly used in:

• Hardware programming
• Embedded systems
• Multithreading
• Operating systems

The volatile keyword prevents the compiler from making optimizations to that variable.

12. What are Function Pointers in C?

A function pointer stores the memory address of a function.

Function Pointers are mainly used for:

• Callback functions
• Dynamic function calls
• Event handling

They allow functions to be passed as arguments to functions.

13. What is a Friend Class/Function?

A Friend Function or Friend Class can access the protected members of another class.

Important points are:

• Declared using the friend keyword.
• Breaks access restrictions.
• Useful for operator overloading and helper functions.

Friendship should be used carefully to keep the data safe.

14. What is a Pure Virtual Function and an Abstract Class?

A Pure Virtual Function is a function declared with = 0.

For example:

• virtual void display() = 0;

A class that has at least one Pure Virtual Function becomes an Abstract Class.

Key points are:

• Abstract Classes cannot be instantiated.
• Used to define interfaces.
• Supports runtime polymorphism.

15. What are Templates in C++?

Templates are a feature in C++ that allows functions and classes to work with data types without rewriting code.

The benefits of Templates are:

• Code reusability
• Reduced duplication
• Better flexibility
• Compile-time polymorphism

Templates play a key role in the Standard Template Library (STL).

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Conclusion

In conclusion, C and C++ are powerful programming languages. They are the base of modern software systems. C is used more for system-level programming. This is due to its speed and efficiency. C++ is different. It has object-oriented features. These features help build complex applications. To do well in interviews, you need to understand some concepts. These concepts include pointers, memory management, object-oriented programming (OOP), and new features in C++. This guide is here to help. It has C and C++ interview questions and answers. It is for beginners who want to learn the basics and feel confident in interviews. This helps you prepare thoroughly for interviews on C and C++. Get expert career guidance from our Training and Placement Institute in Chennai.