24 General & Language-Specific Coding Interview Questions

All businesses are at least partly digital now, so all businesses need coders. They are the developers and engineers who maintain the internal systems, sales websites, mobile apps and customer interfaces that keep your business running.

Coding skills are in high demand. However, it is specialised and technical, so your otherwise excellent HR team may not know what to look for when hiring. If this is the case, have your tech managers join the interviews, and make sure they are properly briefed on the protocol for answering questions about the company.

Are you hiring other IT professionals? Check out our general programming interview questions guide.

We divided these sample questions into two sets: general questions for all jobseekers, and sample ones per language. Use these questions to assess potential hires’ theoretical knowledge, practical coding skills, and ability to communicate and work well with others.

You can also use these examples of coding interview questions to focus your interview. Too many unrelated questions waste time and may not get you the information you need.

Before you roll out these questions, however, make sure your HR group has a good understanding of the programming language and skills required by the position and the kind of coding problems your new hire will face. You should also clarify the expectations for junior and senior coders with your tech team. Many teams expect engineers to have a computer science degree + actual IT experience.

Coding is partly technical, but can also be approached in different ways. These questions give you an idea of the candidate’s approach and methods, and whether they can blend with those of your team.

What is your preferred programming language and why? How would you improve it? What you learn from this: Coders need to use and understand several programming languages, so that they can choose which to use for a given project. Even if they prefer a different language to the one you need, you’ll see whether they are flexible and knowledgeable enough to shift.

Please share your major project process, from briefing to delivery. Speaking broadly (in case it’s confidential), what was the central problem and how did you solve it? What you learn from this: First, you’ll see how much practical project experience the coder has, and how involved they were in actually solving the problem. (How well do they understand the solution?) Second, coders must not only be able to propose solutions but clearly explain the logic behind them.

How would you debug an essential program while it’s in use? What you learn from this: Troubleshooting a program while it’s in use (for example, during peak business hours) is a core skill for an IT team. Is their first instinct to run a debugging program, or to ask questions to isolate the problem and what happened? Again, your interviewee’s answers and thinking should be consistent with that of the larger team.

This is and will always be a stressful job, but teamwork is essential. Tell us about a teamwork issue that you faced and how you solved it. What you learn from this: Coders must work in sync with others despite individual differences, to deliver under tough lead times. You’re looking for people who understand and truly accept this, and who have experience recognizing and fixing their areas for improvement.

We have selected questions that assess your interviewees’ experience in some of the more in-demand programming languages. Always consult with your tech team to ensure that the questions are relevant to the role you’re interviewing for.

Javascript What variables are in Javascript? What is the pop() method? What’s closure? How would you create and clone an object? What is your most unusual Javascript project so far?

Python Discuss map, filter and reduce. What is a first-class object? What is a circular dependency, and can you prevent it? Do you use generators? What for?

C What’s the difference between C and C#? How do you decide which one to use? What are the basic data types used by C? What is a static variable? What is the scope of a variable? What are calloc() and malloc()?

Java What is an object factory and when do you use it? What’s the difference between a checked and unchecked exception? What is a Singleton pattern, and how would you run it? Can you run “A extends B, C” in Java?

C# What are arrays? How many basic string operations are there in C#, and what are they? What are boxing and unboxing? Managed and unmanaged pieces of code? What are virtual and abstract methods?

Coders are in perpetual demand, and turnover is high. Use these sample interview questions to hire more efficiently in less time, and to find and retain coders with both the technical and teamwork skills to be an asset to your business.