10 Top C Interview Questions for 2022 (With Sample Answers)

By Indeed Editorial Team

January 13, 2022

If you are a computer programmer who’s looking for their first job in the field, you will first need to know what to expect from a C interview. In many interviews, you might be asked basic and behavioral questions. However, during your C interview, you must display technical knowledge—defining certain terms and performing certain coding functions. In this article, we list common C programming questions a hiring manager might ask you and sample answers to help you prepare your own.

What is C programming?

C is a computer programming language that was developed to write operating systems. Programs that run on C can start up very quickly and because they are standalone programs, they can be transferred to similar machines without the need for source code. Developers who use C programming language can control low-level aspects of a computer’s operations.

How to prepare for a C interview

As part of your preparation for a C interview, you must focus on the following areas:

  • How to define basic C programming terms, like variable, constant and compiler

  • How logical, run-time and syntax errors differ

  • How to use operators. Operators you might use include the semicolon ( ; ), the AND operator (&&) and the OR operator (||).

  • How to discuss your choices as a developer

In addition, you must know how to show your practical knowledge of C programming. In your C interview, you will likely have to write out certain operations, like how to command a computer to print specific messages.

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Common C interview questions and sample answers

Below are 10 of the most commonly asked C interview questions. Most are concerned with basic concepts, but it is important that you can articulate your understanding of the C language and defend the choices you make as a developer.

  1. What is the difference between a variable and a constant?

  2. Describe the functions of a compiler and an interpreter.

  3. What’s the difference between source codes and object codes?

  4. How do logical, run-time, and syntax errors differ?

  5. What is a comment and how do you insert one in a C program?

  6. Should you declare all header files in every C program?

  7. When should the keyword “void” be used in a function?

  8. Why are algorithms vital to C programming?

  9. How can data be sorted in C programming?

  10. When should you use an array instead of individual variables?

1. What is the difference between a variable and a constant?

There is a chance your interviewer might ask you about basic terms and concepts in C programming. Of course, you should know what constants and variables are, but be prepared to explain how they function in the C language.

Example: “A variable is an identifier that is made up of one or more characters (which includes letters, numbers, and certain symbols), and it can be altered throughout the entire program. Like a variable, a constant is an identifier that is made of one or more characters (including letters, numbers, and a few allowable symbols), but a constant’s value may not be changed in the program.”

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2. Describe the functions of a compiler and an interpreter.

In C language, compilers and interpreters both execute program codes, but in different ways. If asked this question, explain how the file execution processes differ and what can stop a compiler or an interpreter from executing a file.

Example: “A compiler executes program codes after checking the syntax of the entire program. However, it will not begin execution if it finds any syntax errors in the program. Like a compiler, an interpreter executes program codes, but an interpreter does so one line at a time. However, if the program encounters a syntax error in the middle of execution, the interpreter will stop executing the file.”

3. What’s the difference between source codes and object codes?

During your C programming interview, you may need to talk about source codes, object codes and how those codes are produced. You will also be required to show your understanding of different file extensions.

Example: “Source codes are written by the programmer and they are saved with the extension .C. These codes contain the commands and keywords that instruct the computer. However, a compiler is needed to translate source code into a language the computer can understand, which results in object codes. Object codes are saved with the.OBJ file extension.”

4. How do logical, run-time, and syntax errors differ?

If the hiring manager poses this question to you during your C interview, all you might have to do is to define each type of error, explain why they occur and talk about how they affect a program.

Example: “A logical error is one that might pass the compilation process but produce an unexpected output. Logical errors occur when a programmer uses the wrong formula or a wrong sequence of commands.

A run-time error is one that occurs while the program is being executed. This causes the program execution to pause and show which program line caused the error.

A syntax error occurs when a coder makes mistakes in programming, like misplacing a symbol, forgetting to use a symbol where one is needed, misspelling a command or using the wrong case for a command.”

5. What is a comment and how do you insert one in a C program?

Comments are helpful tools programmers use to point out particular bits of code in a program for debugging and to justify the code’s existence. If you get this question during your C interview, define what a comment is in the C language and how you can insert one.

Some developers decide to put comment symbols (/* */) around some of their codes to help themselves or other developers who need to debug a program. Whether or not that is your preference, you should discuss why developers decide to use comment symbols.

Example: “A comment in C programming can serve as several things, including an explanation of why a certain code or function was placed in a program or a description of what the program is about. In order to insert a comment into a program, I can place text inside and surround that text with the /* */ characters (the comment begins with /* and ends with */). I can place comments anywhere in the program.

When I choose to put comment symbols around some of my coding, I do that to aid in debugging. In case sections are in fact causing errors in the program, those codes could be addressed. If the coding is correct, the comment symbols can be removed. This will save me time because I won’t have to retype any correct coding that I otherwise would have deleted.”

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6. Should you declare all header files in every C program?

If you encounter this question, simply say that you do not need to declare all header files in every C program you write and discuss the reasons why.

Example: “I do not need to declare all header files in every C program I write. I would only need to declare header files in each C program based on the commands and functions I will be using in that program. Each header fill has a different prototype and different function definitions, and declaring all header files would unnecessarily increase the file size and load of the program.”

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7. When should the keyword “void” be used in a function?

In C programing “void” (written in all lowercase) is a keyword you can use when the function you use will not return a value. Discuss where and when you will use the keyword.

Example: “I must decide whether a function will be returning a value when I declare it. When that function will not return a value, I use the keyword “void” by placing it in the leftmost part of the function header.”

8. Why are algorithms vital to C programming?

Algorithms essentially carry a list of steps that computers need to follow specific procedures. As part of your answer to this question, you can discuss the three purposes of creating an algorithm before you create a program.

Example: “I must create an algorithm before I can create a C program because the algorithm provides a roadmap for how to arrive at a solution, it acts as a blueprint for how the program will start and it determines which processes and computations will be involved.”

9. How can data be sorted in C programming?

Show that you know that there are generally two ways to sort data in C programming, one being the gsort() function.

Example: “I can sort data in C programming with the built-in gsort() function. Alternatively, I can define my own functions for sorting.”

10. When should you use an array instead of individual variables?

If this question is posed to you, discuss why arrays are more practical when storing a set of data in one program.

Example: “Arrays are preferable when storing multiple related data because arrays only need one word, which is followed by an element number. For example, if I was storing the names of 10 basic cloud types, I would only need to use the keyword “cloud” and list them like so: cloud[0], cloud[1], cloud[2], cloud[3] … cloud[9]. If I’m using individual variables, each would have a different name based on the number (cloud1, cloud2, cloud3 … cloud 10).”

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