Top 20 C Programming Language Interview Questions: Prepare for Success!

Neha Rawat

Feb 13, 2024
Top 20 C Programming Language Interview Questions: Prepare

Master essential C programming concepts with these top 20 interview questions. Ace your interviews and secure success in C programming roles.

C programming language is one of the most widely used programming languages in the world. Developed by Dennis Ritchie in the early 1970s, C has become the foundation for many other programming languages due to its efficiency and flexibility. Understanding C programming is essential for anyone pursuing a career in software development.

Importance of C Programming Language in Interviews

In technical interviews for software development roles, proficiency in C programming is often a requirement. Employers seek candidates who not only have a strong grasp of fundamental programming concepts but also demonstrate proficiency in C due to its widespread use in systems programming, embedded systems, and low-level programming.

1. Basic Concepts in C Programming

1.1 Variables and Data Types

In C programming, variables are used to store data, and they must be declared before use. Common data types in C include int, float, char, and double.

1.2 Control Structures

Control structures such as if-else statements, loops (for, while, do-while), and switch statements are used to control the flow of execution in a C program.

1.3 Functions

Functions in C allow for modular programming by breaking down tasks into smaller, reusable blocks of code. They consist of a function declaration, function definition, and function call.

Commonly Asked Interview Questions

Question 1: What is the difference between printf() and scanf() functions?

printf() is used to print formatted output to the screen, while scanf() is used to read formatted input from the user.

Question 2: Explain the difference between malloc() and calloc().

malloc() is used to allocate memory dynamically, while calloc() is used to allocate memory dynamically and initialize all bytes to zero.

Question 3: What is the purpose of #include ?

#include is a preprocessor directive that tells the compiler to include the standard input-output library in the program.

Question 4: How is a pointer variable declared?

A pointer variable is declared by adding an asterisk (*) before the variable name. For example, int *ptr; declares a pointer to an integer.

Question 5: Explain the concept of recursion.

Recursion is a programming technique where a function calls itself to solve a problem. It consists of a base case and a recursive case.

2. Intermediate Concepts in C Programming

2.1 Arrays and Strings

Arrays are collections of elements of the same data type, while strings are arrays of characters terminated by a null character ('\0').

2.2 Pointers and Memory Management

Pointers are variables that store memory addresses. They are used for dynamic memory allocation and manipulation of memory addresses.

2.3 Structures and Unions

Structures allow for the creation of user-defined data types by grouping related variables together. Unions are similar to structures but share memory locations for their members.

3. Advanced Concepts in C Programming

3.1 File Handling

File handling in C involves operations such as opening, reading, writing, and closing files. Standard library functions like fopen(), fclose(), fread(), and fwrite() are used for file handling.

3.2 Dynamic Memory Allocation

Dynamic memory allocation allows for the allocation and deallocation of memory during program execution using functions like malloc(), calloc(), realloc(), and free().

3.3 Preprocessor Directives

Preprocessor directives in C begin with a hash symbol (#) and are processed before the compilation of the program. They are used for macro definitions, file inclusion, and conditional compilation.

Advanced Interview Questions

Question 6: What is the difference between strcpy() and strncpy()?

strcpy() copies a string from source to destination until it encounters a null character, while strncpy() copies a specified number of characters from source to destination.

Question 7: Explain the use of volatile keyword in C.

The volatile keyword is used to indicate that a variable may be changed unexpectedly by external factors, such as hardware interrupts or concurrent threads.

Question 8: How is a function pointer declared?

A function pointer is declared by specifying the return type and parameters of the function it points to. For example, int (*ptr)(int, int); declares a function pointer that points to a function taking two integers as arguments and returning an integer.

Question 9: What are the differences between calloc() and realloc()?

calloc() allocates memory and initializes it to zero, while realloc() reallocates memory for an existing block, optionally copying the old data to the new block.

Question 10: Explain the purpose of the register keyword.

The register keyword is used to suggest to the compiler that a variable be stored in a CPU register for faster access.

Tips for Acing C Programming Interviews

To excel in C programming interviews, it is essential to:

  • Practice coding problems related to C programming.

  • Review fundamental data structures and algorithms.

  • Stay updated with the latest features and best practices in C programming.


Preparing for C programming language interviews requires a solid understanding of fundamental concepts, as well as practice solving coding problems. By mastering the topics covered in this article and practicing regularly, you can increase your chances of success in C programming interviews.

FAQs (Frequently Asked Questions)

Q1. How should I prepare for a C programming interview?

A1: To prepare for a C programming interview, review fundamental concepts, practice coding problems, and familiarize yourself with common interview questions.

Q2. Are there any online resources for practicing C programming interview questions?

A2: Yes, there are several online platforms such as LeetCode, HackerRank, and GeeksforGeeks that offer practice problems and interview questions for C programming.

Q3. What are some common mistakes to avoid during a C programming interview?

A3: Common mistakes to avoid include neglecting to check for NULL pointers, forgetting to free dynamically allocated memory, and not understanding the time and space complexity of your code.

Q4. How important is knowledge of C programming for software development roles?

A4: Knowledge of C programming is essential for certain software development roles, particularly those involving systems programming, embedded systems, and low-level programming.

Q5. Can I use C programming language for web development?

A5: While C programming is not commonly used for web development due to its low-level nature, it can still be used for server-side programming and developing web servers.

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