C/CPP Interview Questions

 

✅ C & C++ Interview Question Bank (With Answers)

🔹 SECTION 1: C LANGUAGE (Core)

Q1. What is the difference between malloc() and calloc()?

Answer:

malloc calloc

Allocates memory Allocates & initializes to zero

Faster Slightly slower

Takes 1 argument Takes 2 arguments

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Q2. What is a dangling pointer?

Answer:

A pointer that points to a memory location that has been freed or gone out of scope.

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Q3. Difference between const int *p and int *const p?

Answer:

• const int *p → value cannot be changed

• int *const p → pointer cannot be changed

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Q4. What is static keyword used for?

Answer:

• Preserves variable value between function calls

• Limits scope to file when used globally

• Shares value across objects in C++

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Q5. What is volatile keyword?

Answer:

Tells compiler not to optimize variable since it can change externally (used in hardware registers, ISR).

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Q6. What is segmentation fault?

Answer:

Accessing invalid or unauthorized memory location.

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Q7. What is structure padding?

Answer:

Extra bytes added by compiler to align data for faster access.

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Q8. What is difference between stack and heap?

Answer:

Stack Heap

Automatic allocation Manual allocation

Faster Slower

Limited size Larger size

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🔹 SECTION 2: POINTERS (Very Important)

Q9. What is pointer to pointer?

Answer:

A pointer that stores address of another pointer.

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Q10. What is NULL pointer?

Answer:

Pointer that points to nothing (NULL or 0x0).

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Q11. What is function pointer?

Answer:

A pointer that points to a function’s address.

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Q12. Difference between array and pointer?

Answer:

• Array name is constant

• Pointer can be reassigned

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🔹 SECTION 3: C++ BASICS

Q13. What is OOP?

Answer:

Programming model based on Object, Class, Encapsulation, Inheritance, Polymorphism, Abstraction.

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Q14. Difference between C and C++?

Answer:

• C → procedural

• C++ → object oriented

• C++ supports classes, inheritance, STL

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Q15. What is constructor?

Answer:

Special function automatically called when object is created.

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Q16. What is destructor?

Answer:

Function called automatically when object is destroyed.

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Q17. Can constructor be private?

Answer:

Yes (used in Singleton pattern).

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Q18. What is copy constructor?

Answer:

Initializes object using another object of same class.

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Q19. What is virtual function?

Answer:

Function that supports runtime polymorphism using base class pointer.

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Q20. What is virtual destructor?

Answer:

Ensures proper cleanup of derived class object.

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🔹 SECTION 4: OOP CONCEPTS

Q21. What is encapsulation?

Answer:

Binding data and methods together and hiding internal details.

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Q22. What is inheritance?

Answer:

Derived class inherits properties of base class.

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Q23. What is polymorphism?

Answer:

Same function name behaving differently.

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Q24. Difference between compile time and runtime polymorphism?

Answer:

• Compile time → function overloading

• Runtime → function overriding

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Q25. What is abstraction?

Answer:

Showing only essential features, hiding implementation.

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🔹 SECTION 5: ADVANCED C++

Q26. What is STL?

Answer:

Standard Template Library providing containers, algorithms, iterators.

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Q27. Difference between vector and list?

Answer:

vector list

Contiguous memory Non-contiguous

Fast access Slow access

Slow insertion Fast insertion

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Q28. What is smart pointer?

Answer:

Pointer that automatically manages memory.

Examples:

• unique_ptr

• shared_ptr

• weak_ptr

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Q29. What is RAII?

Answer:

Resource Acquisition Is Initialization — resource tied to object lifetime.

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Q30. What is namespace?

Answer:

Used to avoid name conflicts.

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🔹 SECTION 6: EMBEDDED / SYSTEM C & C++

Q31. Why use volatile in embedded systems?

Answer:

Variables can change due to hardware or interrupts.

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Q32. What is ISR?

Answer:

Interrupt Service Routine — function executed on interrupt.

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Q33. What is memory leak?

Answer:

Allocated memory not freed.

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Q34. Difference between new/delete and malloc/free?

Answer:

• new/delete call constructors/destructors

• malloc/free do not

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Q35. What is deadlock?

Answer:

Two processes waiting for each other indefinitely.

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🔹 SECTION 7: COMMON TRICK QUESTIONS

Q36. Can main() be overloaded?

Answer:

No.

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Q37. Can we have virtual constructor?

Answer:

No, but destructor can be virtual.

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Q38. Can sizeof return zero?

Answer:

No.

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Q39. Is C pass by value or reference?

Answer:

C supports only pass by value (reference via pointers).

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Q40. Why sizeof(char) is always 1?

Answer:

Defined by C standard.

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