5 Common C++ Interview Questions (With Example Answers)
By Indeed Editorial Team
Updated August 11, 2022
Published December 12, 2019
The Indeed Editorial Team comprises a diverse and talented team of writers, researchers and subject matter experts equipped with Indeed's data and insights to deliver useful tips to help guide your career journey.
There is no shortage of work for C++ programmers since many companies that work with low-level systems or develop high-performance software require staff with C++ programming skills. This programming language is foundational, so it is in high demand. A career as a C++ programmer remains a very viable option.
In this article, you’ll learn what to expect from a C++ interview and how to answer sample C++ interview questions with example answers.
What does a C++ interview look like?
C++ is a foundational coding language that has remained popular despite changing trends in software development and design. C++ is one of the harder languages to master, so if you’re being asked C++ interview questions, you can expect them to be technical to fully demonstrate your understanding of this complex development language.
Candidates who know C++ are valuable, as it is likely that they will also know coding in several easier languages, some of which were likely modeled after certain elements of C++. Interviewers looking for C++ proficient candidates will use questions targeted at establishing that you have a basic understanding of the language and how you’ve used it.
If you’re preparing for C++ interview questions and answers, consider opportunities to use the STAR method of answering interview questions. Using STAR, you can outline a situation that occurred, define your role in solving it, what actions were your responsibility and the ultimate resolution.
Learn More: How To Use the STAR Interview Response Technique
Common C++ interview questions and topics
While there are many questions you may be asked in a C++ interview, some common ones include:
1. What are vectors?
A thorough answer to this question would display a basic understanding of C++ by going beyond defining vectors to also make comparisons to other common data structures. This shows an understanding of concepts beyond that of vectors, such as dynamic arrays.
Example: “A vector is a type of data-structure sequence container that is very similar to a dynamic array. Just like in an array, vector elements are placed in contiguous storage, which means that they can be accessed and traversed using iterators. Unlike arrays, however, the size of vectors can change dynamically and is automatically handled by the container.
Vectors are very efficient compared to other dynamic sequence containers, such as lists and forward lists, when it comes to accessing their elements, and relatively efficient about adding or removing elements that are placed at the end. However, when it comes to operations that involve inserting or removing elements at other positions, such as the beginning or middle, vectors don’t perform that well.”
2. What are the differences between C and C++?
A question that asks, “What’s the difference? ...” is a good tool for interviewers to test the basic knowledge of a potential employee on dual disciplines. Since the question is asking the difference between two things, describing both of them in the answer displays that you have a good handle on both.
These questions are easy to generate in technology interviews because there are so many nuanced processes, methods and objects that IT professionals encounter daily. For C++, some what’s-the-difference question topics may include:
References versus pointers
Copy versus deep copy
Default constructor versus copy constructor
Constructor versus deconstructor
Example: “C is a procedural language, whereas C++ is both a procedural and an object-oriented language. In this way, C++ can be referred to as a hybrid language. C++ is a superset of C, which means that C++ can run most of C code, but not the other way around.
Because C++ is also an object-oriented language, it supports functions like templates, inheritance, function overloading, and virtual functions, whereas C does not. Because C is a procedural language, data and functions are separate and free entities, whereas in C++ the process of encapsulation means that data and functions are merged to form objects.
In C data can be manipulated by outside code, whereas the process of encapsulation in C++ ensures that data structures and operators are used in a certain way. C does not have a namespace feature, whereas C++ uses it to avoid collisions. C does not provide direct support for exception handling, whereas C++ does.”
3. Compare and contrast structure and class in C++
Much like what’s-the-difference questions, questions that ask you to compare and contrast two items allow you to share your knowledge of two distinctly different features that share some commonality, This question gauges your technical knowledge of data types in C++. When asked to define and share differences, the response should be more technical and definitive than practical.
Example: “A class is a user-defined data type that combines data and its related functions into one unit, in this way enabling the processes of data abstraction and inheritance. A structure is also a user-defined data type, but it possesses its own operations and is mainly used to group data. The main difference between the two, however, is that structure members have public access by default, whereas class members have private access.”
4. Explain how constructors and deconstructors work together in C++
This question requires a clear, definitive response. There’s a lot to discuss when it comes to constructors and deconstructors in C++, so this response may be best delivered in multiple pieces.
First, define constructors and what they do. Consider describing the types of constructors that exist in C++. Then, define deconstructors and explain the correlation to constructors.
Example: “A constructor is a special function within the class that is called by the compiler every time a new object is created, as it initializes the object by assigning a value to it. A constructor is named the same as the class, will never have a return type, and can either be defined within the class or outside of the class by using the operator. C++ allows for the overloading of the constructor, which means that there can be more than one constructor for a given class, as long as they have differing parameters.
Some of the main types of constructors include:
Default constructor: If a user doesn’t supply a constructor for a class, a default constructor is provided by the compiler. These kinds of constructors don't have parameters.
Parameterized constructor: This type of constructor does have parameters. By passing the appropriate values as arguments, a parameterized constructor provides different values to different objects.
Copy constructor: This type of constructor takes an object as an argument and is used to create a copy of an existing object of the same class.
Conversion constructor: This is a single-parameter constructor that is used for conversion of type, as the type of the first parameter is converted to the class type.
Move constructor: This type of constructor allows for the resources of an R-value object to be moved into an L-value without copying.
A destructor does the opposite of what a constructor does. When an object passes out of scope or is deleted, a destructor destroys the object by unallocating memory and doing other cleanup tasks. As is the case with the constructor, a destructor has the same name as the class, except it gets a tilde prefixed and has no argument or return value. If no destructor is defined by a user for a class, the compiler will implicitly declare one.”
5. Explain what an inline function is and how to use it
Any question that asks how to do something can often be answered from personal experience. To answer this question thoroughly, define an inline function, talk about some of its benefits and describe a personal experience with it using the STAR method of answering interview questions.
Example: “An inline function instructs the compiler to insert a copy of the code of that function whenever that function is called. To make a function inline, the keyword “inline” is placed before the name of the function, and the function is defined before any calls are made to it.
Some benefits of using an inline function are:
It reduces function call overhead.
It reduces push/pop variable overhead on the stack when a function is called.
You can allow for the compiler to execute context-specific optimization on the body of a function when you inline it, whereas with a normal function call this cannot be done.
If it is small, inline functions can be effective in embedded systems as they yield less code.
When I was a developer at Ragisberg, I used C++ to create their internal applications. At one point I was tasked with reducing overhead for small, commonly used functions that were taking too long to call. I did this by deploying inline functions. As a result, the function call was able to happen a lot faster because the overhead was eliminated.”
Tips for your next C++ interview
The above questions give you an idea of technical questions you should expect in an IT interview where C++ might be involved. You should, however, also expect questions that are not specifically related to C++ programming, in which the interviewer will try to gauge soft skills like whether you’ll be a good team player and how you would cope in stressful situations.
Additionally, it’s advisable to also prepare for behavioral interview questions. Lastly, there are a few general tips that you can remember if you want to have a good interview, such as:
Arrive about 15 minutes before your appointment time.
Answer questions as honestly as you can.
Bring along copies of your CV and also have a pen and notebook handy.
Ask the interviewer questions about the job, policies and the company at large.
Do research on the company before the interview.
Do not speak negatively about previous employers or positions.
Consider your body posture and facial expressions during the interview, as it tells the interviewer more about you than you may think.
Try to come across as confident but also friendly.
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