C++ Interview Preparation | STL Problems, OOP Design, Debugging, Optimization Tips

This tutorial on C++ Interview Preparation covers commonly asked interview questions, STL-based problems, object-oriented design questions, debugging, optimization tips, and common pitfalls. It helps learners prepare effectively for technical interviews in C++ and demonstrate strong programming skills.

C++ Interview Preparation – Complete Guide

1. Common C++ Interview Questions

Core C++:

  1. Difference between C and C++
  2. new vs malloc
  3. stack vs heap memory
  4. Copy constructor vs assignment operator
  5. Shallow vs deep copy
  6. virtual keyword and polymorphism
  7. const correctness

Object-Oriented Programming:

  1. Difference between class and struct
  2. Access specifiers and encapsulation
  3. Inheritance types (single, multiple, multilevel)
  4. Virtual functions and vtable
  5. Abstract classes and interfaces

STL & Containers:

  1. Differences between vector, list, deque
  2. Map vs unordered_map
  3. Stack, queue, priority_queue use cases
  4. Iterator types and usage
  5. Lambda functions and functors

Advanced Concepts:

  1. Smart pointers (unique_ptr, shared_ptr)
  2. Move semantics and rvalue references
  3. Exception handling best practices
  4. Multithreading, mutex, atomic operations

2. Common Pitfalls

  1. Forgetting to delete dynamically allocated memory → memory leaks
  2. Using shallow copy instead of deep copy for objects with pointers
  3. Ignoring const correctness in functions
  4. Overusing global variables
  5. Incorrect mutex/lock usage in multithreading
  6. Misusing STL iterators (dangling iterators, invalidation)

3. STL-based Problems

  1. Reverse a vector or string
  2. Find the maximum frequency element using unordered_map
  3. Merge two sorted arrays using STL algorithms
  4. Implement a stack or queue using deque
  5. Use priority_queue for top-K problems

Example – Maximum Frequency Element


#include <iostream>
#include <unordered_map>
#include <vector>
using namespace std;

int main() {
vector<int> v = {1,2,2,3,3,3,4};
unordered_map<int,int> freq;
for(int x : v) freq[x]++;
int maxFreq = 0, element;
for(auto& p : freq) {
if(p.second > maxFreq) {
maxFreq = p.second;
element = p.first;
}
}
cout << "Max frequency element: " << element << endl;
}

4. Object-Oriented Design Questions

Example Topics:

  1. Design a Parking Lot system
  2. Implement Library Management System
  3. Design a Bank Account system with multiple account types
  4. Explain Singleton vs Factory patterns
  5. Discuss Observer pattern in real-world use cases

Tips:

  1. Draw UML diagrams before coding
  2. Identify classes, objects, inheritance, and relationships
  3. Focus on clean, modular, and reusable code

5. Debugging and Optimization Tips

Debugging:

  1. Use gdb or IDE debugger
  2. Print intermediate values
  3. Check for memory leaks using tools like Valgrind
  4. Step through code to catch logical errors

Optimization:

  1. Prefer references over copies for large objects
  2. Use move semantics where possible
  3. Prefer unordered_map over map for faster access
  4. Avoid unnecessary dynamic memory allocations in loops
  5. Minimize complexity of algorithms (O(n log n) instead of O(n²))

Best Practices for Interviews

  1. Understand core C++ concepts thoroughly
  2. Practice STL problems daily
  3. Be ready to design small systems using OOP
  4. Discuss time/space complexity for every solution
  5. Write clean, readable code and handle edge cases

Summary

This chapter covers C++ Interview Preparation, including:

  1. Frequently asked interview questions
  2. STL-based problems and solutions
  3. Object-oriented design problem-solving
  4. Debugging and optimization techniques
  5. Common pitfalls and best practices

Following this guide ensures you are well-prepared to answer technical questions confidently and demonstrate strong C++ programming skills.