Extremely trivial C++ phone interview question [closed]

Question

My company is currently interviewing for a developer position, and a disturbingly high number of candidates with good resumes end up being total frauds. We do have a written technical test which works fine for that purpose (it was initially designed for interns, but we found out that even candidates interviewing for senior positions failed it abysmally), but I'd like a few questions that allows us to filter out those people with a < 10 min. time investment.

I'm trying to come up with a very trivial C++ (or even just programming) question that can be easily answered on the phone. The goal is not to get tricky, or even midly complex, just to weed out the people who'd fail an "intro to programming" midterm.

So far, the best I've come up with is "Let's assume I'm an intern you're mentoring: can you explain to me, in simple terms, the difference between a vector and a list, and when I should use or the other". Any other ideas?

Answer 1

"What does the copy constructor do" is my favorite interview question. But I think this will get closed as OT.

Answer 2

This is from an intro to programming course:

Assuming you had a string of characters, count how many times each letter is used and print out the least used and most used ones?

But it might not be the best question to ask for someone you are going to eventually be paying.

Just my 2c.

Answer 3

"What does explicit in front of a constructor declaration mean, and when would you use it?"

Answer 4

• What is a const member function.
• What is a static member variable.
• How do you make a member function pure virtual.
• What is a dynamic_cast.
• What is the difference between new and placement new
• When can/should you explicitly call a constructor.
• What is a member initializer list
• What is the difference between a reference and a pointer
• What does & mean in various contexts.
• Why should a template function be defined in the same file it is declared.

All of these should be easy to do over the phone, and would at least give you an idea whether the candidate is a waste of time or not.

If you want generic programmer questions, not c++ specific, try some of these:

• What is polymorphism.
• What is overriding and overloading.
• What is heap and stack.
• Describe the process to take a single-file hello-world source file and make it into an executable.
• What is a hash table.
• What is a linked list. Why would you prefer to use this rather than e.g. an array.
• Describe the binary search algorithm

Answer 5

Here are some simple ones:

• What is passing by reference?
• What does malloc() do?
• What is overloading?

Answer 6

Have you read about the FizzBuzz test? Over the phone you may not want to go character by character but the person should be able to describe the general algorithm to you.

Fizz Buzz Test

Answer 7

I do something similar, I generally start by asking how familiar they are with C++ and then ask a couple basic syntax questions. Starting with basic ones then moving towards more complex. The complex one tend to be less important (I don't really care if the candidate knows the answer) but how they answer the question can help you infer how comfortable with C++ they are.

• What is a class?
• Name a few container types (then I follow up with asking them to compair and contrast the uses)
• What is a polymorphism
  • What is a virtual table? Where is it?
• What is the difference between malloc + new?

I also ask about STL types and templates. I find the best questions are the ones I can come up with off the top of my head because they have come up in day to day work. Which tends to mean they will be more relevant to how well the candidate with handle the job.

Answer 8

What is a virtual destructor and when should you use it ?

Answer 9

The questions about features of the language are apt to fall into 2 groups: those that are so esoteric that a good candidate might not know them, or those that are so simple that a candidate might cram for the interview and get them right without actually understanding them. If you want to know if someone can actually program, ask them to write a program. Obviously this is harder over the phone, so you have to make it trivially simple.

My candidate for a trivial programming question would be "Write a short code fragment to display the first 10 odd numbers". Anybody who couldn't answer that in 60 seconds wouldn't be worth wasting another 9 minutes on.

Answer 10

These three have weeded out "experienced" developers for me recently:

What are the four explicit casts in C++ and when would you use them?

This identifies those who write C-code but think they're writing C++.

What is the difference between a struct and a class?

This identifies those who have come from C# but think that C++ is just syntactically different.

How would you convert a std::string to uppercase?

If you've ten years' experience with STL you'll know that there is no std::string::toupper() and you have probably come across std::transform().

Answer 11

From my personal experience I would say dont take telephonic interviews, atleast not if the guy is in the same ciy. Ive interviewd people who are pretty good on telephonic interviews but flop miserably in a F2F . The telephone gives them a sense of security and they answer questions better than when they face the interiviewer directly.

Answer 12

I've had great success in giving candidates a more substantial problem to solve (focused around design, algorithm, style and testing) before I even meet them.

Typically I get hassled by recruitment consultants who all seem to have perfect candidates for whatever I'm looking for. To them I just hand out the test, tell them the candidate needs to get me their source code in n days (i'm not too strict with the time spent), and if I like it and their CV I'll organise an interview. I think I eliminate (waving arms in the air type numbers) about 95% of fail boats that I would have otherwise spent hours (ie $$$) vetting.

This way I essentially invest zero time in useless candidates. I have an array of problems to give out and I'm now very quick at assessing them. I have even partially scripted the assessement with complexity measures and other metrics.

Answer 13

I've been doing a lot of interviews lately and one thing that kinda bugs me is that if a person never used dynamic_cast or explicit constructor, that doesn't necessarily make him a bad programmer. Recently I read a quote that said, "C++ is a great language if you use 80% of it, the problem is that every developer uses different 80%". Personally, just to list few things, I've implemented delegate-like behavior, extended Boost pool library using my own template meta-programming classes and recently dissected Boost MSM library almost line by line, but if you ask me if I remember of the top of my head if std::string has toupper() method, there's a 50% chance I'd fail your interview.

So I wanted to turn the interview around, leave it open ended, and let the interviewee demonstrate how deep he got into the language without me picking and choosing very specific questions. What do you guys think of this:

What is the most complex/interesting thing of C++ language you have ever used? Then I'd poke around the question to see if the person really knows whatever topic they picked.

Answer 14

Simple question to test critical thinking, rather than C++:

You have a list of increasing numbers given to you (of unknown size), which you can randomly access. You need to find where a particular number occurs.

What's the fastest way of finding the position of the number?

To which a good answer would likely be a description of "Gallop search" (test element 1, then element 2, then 4, 8, etc.; then binary search when you exceed the number). Obviously, they don't need to get the name right, but they'd better give you a nonlinear algorithm.

Answer 15

I prefer asking the following questions during a phone interview:

• How would you swap two integers without using a third variable?
• You have a list of phone book entries (names and numbers), what data structure would you use to store this information, assuming you only need to look up numbers based on person's name, but you don't have to add new entries to the phonebook or remove the old ones? Bonus question: how would your structure change if I said you also need to be able to insert/delete entries efficiently?
• What is a singly linked list? What is an array? Bring examples of situations in which a linked list performs better than an array. Bring examples when array is better than a linked list. Bonus question: describe an algorithm to print the elements of a singly linked list in reverse order.
• Name a couple of sorting algorithms you know. Describe any of them. How efficient is your algorithm of choice?

Note how I don't ask language-specific questions (e.g. name the STL containers, how do you think std::map is implemented, etc.). Those can be asked later, during the on-site interview, when the candidate proves that he's competent enough.

Answer 16

It is not unreasonable to expect people to have an internet connection nowadays.

During the phone screen get them to sit in front of a computer and connect to a site like collabedit then you can ask them real coding questions and see the code they produce real time.