25 Interview Questions On C: A Comprehensive Guide for Success

Are you preparing for a job interview that focuses on the C programming language? Look no further! In this comprehensive guide, we will provide you with 25 interview questions on C that will help you ace your interview and impress your potential employers.

Whether you are a seasoned programmer or just starting your career in software development, these questions will cover various aspects of C and test your knowledge and problem-solving skills.

So, let’s dive right in and explore these essential interview questions on c!

Also Read: Boost Python Code Efficiency: Eliminating Loops for Enhanced Performance


C is a powerful and widely used programming language known for its efficiency and flexibility.

Numerous software systems have built their foundation on it, and it continues to find extensive use in various domains, including operating systems, embedded systems, and game development.

With its low-level capabilities and vast libraries, mastering C can open doors to exciting career opportunities in the tech industry.

25 Interview Questions On C

1. What is the difference between malloc() and calloc() functions?

The malloc() and calloc() are both used to dynamically allocate memory in C, but they have a few differences.

While malloc() allocates memory without initializing it, calloc() not only allocates memory but also initializes it to zero.

The calloc() function takes two arguments: the number of elements to allocate and the size of each element.

2. Explain the concept of pointers in C.

Pointers are variables that store memory addresses.

In C, people widely use them for various purposes, such as accessing and manipulating data indirectly, dynamically allocating memory, and implementing data structures.

Pointers allow efficient memory management and can significantly enhance the performance of programs.

Also Read: Factorial Program in C Programming

3. What is the difference between const and volatile in C?

The const is a keyword used to declare constants that cannot be modified, ensuring the immutability of variables.

Programmer can use ‘volatile’ to indicate that external factors such as hardware interrupts or concurrent threads can change the value of a variable unexpectedly It informs the compiler not to optimize or cache the variable excessively.

4. How does the sizeof() operator work in C?

In C, programmers use the sizeof() operator to actively determine the size, in bytes, of a variable or data type.

It allows programmers to write portable code that adapts to different system architectures.

For example, sizeof(int) returns the size of an integer in bytes.

5. Explain the difference between ++i and i++ in C.

In C, ++i and i++ are both increment operators.

The main difference lies in the order of operations. ++i is a prefix increment operator, which first increments the value of i and then returns the updated value.

On the other hand, i++ is a postfix increment operator, which returns the current value of i and then increments it.

Also Read: C Program to Find the Sum of Cubes of Elements in an Array

6. How can you swap the values of two variables without using a temporary variable?

You can achieve swapping the values of two variables without using a temporary variable by using the XOR bitwise operator.

Here’s an example:

void swap(int* a, int* b) {
    *a = *a ^ *b;
    *b = *a ^ *b;
    *a = *a ^ *b;

7. What is the purpose of the static keyword in C?

In C, the static keyword has different meanings depending on its context.

When used inside a function, it creates a static local variable that retains its value between function calls.

When used with a global variable, it limits the variable’s scope to the current file, making it accessible only within that file.

8. Explain the concept of recursion in C.

Recursion is a programming technique where a function calls itself to solve a problem.

In C, recursive functions can be used to solve complex problems by breaking them down into simpler subproblems.

However, it’s important to define a base case to terminate the recursive calls, preventing infinite recursion.

Also Read: LCM of Two Numbers in C Programming

9. What is the purpose of the volatile keyword in C?

In C, programmers use the volatile keyword to indicate that external factors such as hardware interrupts or shared memory access may unexpectedly change the value of a variable.

It informs the compiler that the variable should not be optimized or cached excessively, ensuring its proper behavior in certain situations.

10. How does dynamic memory allocation work in C?

Dynamic memory allocation in C is performed using the malloc(), calloc(), and realloc() functions from the standard library.

The malloc() function allocates a block of memory, the calloc() function allocates and initializes memory to zero, and the realloc() function resizes a previously allocated block of memory.

It’s important to deallocate the memory using the free() function to prevent memory leaks.

11. What are the different storage classes in C?

C provides several storage classes, each with its own scope, lifetime, and visibility.

The most commonly used storage classes are auto, static, extern, and register.

The default for local variables is the auto storage class, we use static to create variables with a longer lifetime, global variables use extern, and we use register to suggest storing a variable in a CPU register for faster access.

12. Explain the concept of a structure in C.

In C, a structure is a user-defined data type that allows combining different variables of different types into a single entity.

It enables programmers to represent complex data structures, such as records or objects, by grouping related data together.

Each variable within a structure is called a member.

Also Read: C Program to Remove White Spaces and Comments from a File

13. What is the purpose of the typedef keyword in C?

In C, the typedef keyword creates a new type alias for an existing data type.

It provides a way to give meaningful names to complex data types, making the code more readable and maintainable.

Additionally, typedef can be used to define function pointers, making it easier to work with function pointers in C.

14. Explain the concept of function pointers in C.

Function pointers in C allow storing the address of a function in a variable.

They provide a way to pass functions as arguments to other functions, store them in data structures, and dynamically select functions to be executed at runtime.

Function pointers are especially useful in implementing callbacks and dynamic dispatch.

15. How does the NULL pointer work in C?

The NULL pointer in C is a special value that represents a pointer that does not point to any valid memory address.

People often use it to indicate the absence of a valid pointer. By convention, assigning the value NULL to a pointer indicates that it does not currently point to anything.

16. What are preprocessor directives in C?

The preprocessor processes special instructions in C before compiling the source code.

They begin with a # symbol and provide instructions to manipulate the source code, such as including header files, defining constants, and performing conditional compilation.

17. How can you read and write files in C?

The standard library functions, such as fopen(), fclose(), fread(), fwrite(), etc., perform file operations in C.

To read a file, you can open it in read mode using fopen() and then use functions like fread() or fgets() to read its contents.

Similarly, to write to a file, you open it in write mode using fopen() and use functions like fwrite() or fprintf() to write data into the file.

18. Explain the difference between == and === operators in C.

In C, there is no === operator. Instead, the == operator is used for comparison, checking if two values are equal. The == operator returns 1 if the values are equal and 0 otherwise.

It is important to differentiate it from the assignment operator =, which is used to assign a value to a variable.

19. What are the advantages of using C over other programming languages?

C offers several advantages that make it a popular choice for low-level programming and systems development:

  • Efficiency: C allows close control over hardware resources, resulting in highly efficient code.
  • Portability: C code can be compiled and executed on different platforms with minimal modifications.
  • Vast Libraries: C has a rich collection of libraries that provide ready-made solutions for various tasks.
  • Compatibility: C interfaces well with other languages like C++, enabling seamless integration of codebases.

20. What is the significance of the main() function in C?

The main() function is the entry point of a C program. It is the first function that gets executed when the program starts running.

The main() function is where the program’s execution begins, and it typically contains the program’s logic and other function calls.

21. Explain the concept of bit manipulation in C.

Bit manipulation in C involves manipulating individual bits within variables, typically using bitwise operators such as &, |, ^, and ~.

Bit manipulation is often used to optimize code, perform efficient storage, and manipulate hardware registers at a low level.

22. What are the different types of loops in C?

C provides three types of loops: for, while, and do-while.

The for loop is used when the number of iterations is known beforehand.

The while loop is used when the number of iterations is uncertain but is based on a condition.

The do-while loop is similar to the while loop but ensures that the loop body executes at least once, even if the condition is initially false.

23. How can you handle errors and exceptions in C?

In C, error handling is typically done using return values or error codes.

Functions often return a special value or error code to indicate whether the execution was successful or encountered an error.

Additionally, certain library functions set the errno variable to indicate specific error conditions.

24. What is the purpose of the break and continue statements in C?

In loops and switch statements, we use the break statement to terminate the current loop or switch case and resume execution after the loop or switch.

It is often used when a specific condition is met, and there is no need to continue the iteration.

The continue statement skips the current iteration of a loop and moves to the next iteration.

25. How can you pass arguments to a C program from the command line?

The main() function of a C program can receive command-line arguments using the parameters argc and argv.

The argc parameter represents the number of command-line arguments, while the argv parameter is an array of strings containing the actual arguments passed.

The first element of argv (argv[0]) is the name of the program itself.


1: What is the importance of learning C for programmers?

Learning C is crucial for programmers due to the following reasons:
C is the foundation: Many programming languages and frameworks have been built on top of C, making it essential to understand the underlying concepts.
Efficiency and performance: C allows programmers to write highly optimized and efficient code, making it suitable for resource-intensive tasks and low-level programming.
Embedded systems and operating systems: Developers extensively use C in the development of embedded systems and operating systems, as it enables them to control hardware and perform system-level programming.

2: Is C still relevant in today’s programming landscape?

Absolutely! Despite the emergence of newer programming languages, C remains relevant and widely used in various domains. Its efficiency, portability, and low-level capabilities make it an excellent choice for system-level programming, embedded systems, and performance-critical applications.

3: Are there any online resources to practice C interview questions?

Yes, several online platforms provide resources to practice C interview questions, including coding practice websites, tutorial websites, and forums. Some popular resources include LeetCode, HackerRank, GeeksforGeeks, and Stack Overflow.

4: How can I prepare for a C programming interview?

To prepare for a C programming interview, consider the following steps:
a. Review the fundamentals: Ensure you have a solid understanding of C syntax, data types, control structures, and functions.
b. Practice coding: Solve coding challenges and interview-style questions related to C programming to strengthen your problem-solving skills.
c. Focus on data structures and algorithms: Familiarize yourself with common data structures and algorithms implemented in C.
d. Study specific C concepts: Brush up on topics such as pointers, memory management, file handling, and dynamic memory allocation.
e. Mock interviews: Practice mock interviews to simulate the interview experience and gain confidence in answering technical questions.

5: How can I make my C code more efficient?

To improve the efficiency of your C code, consider the following tips:
a. Optimize algorithms and data structures: Choose the most appropriate algorithm and data structure for the problem at hand.
b. Minimize memory usage: Be mindful of memory allocation and deallocation to avoid memory leaks and excessive memory usage.
c. Use appropriate data types: Choose the smallest data type that can accommodate the required range of values to conserve memory.
d. Avoid unnecessary function calls: Minimize the number of function calls and optimize repetitive computations.
e. Optimize loops: Reduce loop iterations and avoid redundant calculations within loops.
f. Utilize bitwise operations: Bit manipulation can lead to efficient solutions in certain scenarios.


In this article, we have covered 25 essential interview questions on C that can help you prepare for your next C programming interview.

From memory management to pointers, from file handling to recursion, these questions cover various aspects of C programming and will test your understanding and problem-solving skills.

Remember to practice implementing these concepts in real code and to explore additional resources to strengthen your knowledge further.

Good luck with your interview preparation!