Top 30+ C Interview Questions and Answers

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C is a powerful general-purpose programming language created in the early 1970s by Dennis Ritchie at Bell Labs. Originally developed to build the UNIX operating system, C quickly became the foundation for many other languages like C++, Java, and Python. Its speed, simplicity, and flexibility have made it a favourite for system programming and embedded systems even today. If you are preparing for a technical job interview, chances are high you will face questions on C. This blog covers 30+ commonly asked C interview questions to help you prepare easily.

Fun Fact – According to a Statista report, 20.3% of developers use C, making it one of the most used programming language worldwide.

Basic C Interview Questions

Here are some basic-level C language interview questions to help you build a strong foundation before moving to advanced topics.

1. What is C programming language?

C is a foundational programming language used to write everything from operating systems to embedded software. It gives direct control over memory and hardware. C follows a procedural approach, making it ideal for tasks that require performance, structure, and precision. 

2. What are the features of C programming language?

• Simple syntax and easy to learn
• Fast execution and efficient memory use
• Supports structured programming
• Allows direct hardware access
• Portable across platforms with minimal changes

3. What are the different data types in C?

C supports a variety of data types used to store different kinds of values in memory.

• int
• float
• char
• double
• void
• enum (enumerations)
• arrays
• structures
• pointers

4. Explain the concept of pointers and their uses.

A pointer is a variable that stores the address of another variable. I use pointers to pass large data efficiently, work with dynamic memory, and for functions that return multiple values.

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

malloc() allocates memory without initializing it. calloc() allocates and sets all bits to zero. Both return a pointer to the allocated memory.

6. How does the sizeof operator work in C?

sizeof returns the memory size (in bytes) of a data type or variable. It is evaluated at compile-time.

7. What are storage classes in C, and how do they affect variable scope?

Storage classes (auto, static, register, extern) control a variable’s lifetime, default value, memory location, and its visibility within or across functions and files.

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

In functions, static keeps the value between calls. In global context, it limits scope to the file.

Note – Basic C program interview questions include topics like syntax, data types, loops, conditionals, and simple code output.

Also Read - Top 50+ C++ Interview Questions and Answers

C Language Interview Questions for Freshers

Here is a list of commonly asked C interview questions and answers specially selected for freshers to help them crack their first tech interview.

9. What is the difference between a declaration and a definition in C?

A declaration tells the compiler about a variable’s or function’s type. A definition allocates memory. You can declare a variable multiple times but define it only once.

10. How are arrays passed to functions in C?

Arrays are passed by reference. This means when I pass an array, the function receives its memory address—not a full copy. Any changes affect the original array.

11. What is recursion? Provide an example of a recursive function.

Recursion is when a function calls itself. I’ve used it to calculate factorials. For example:

int fact(int n) {  

  if(n==0) return 1;  

  return n * fact(n-1);  

}

12. What is the purpose of header files in C?

Header files contain function declarations and macros. They allow you to reuse code. For example, #include <stdio.h> gives access to printf() and scanf().

13. How does a switch statement work, and when would you use it?

A switch checks a variable against different values. It’s cleaner than many if-else blocks. Each case matches one value and runs its code.

14. Explain the use of the const keyword in variable declarations.

const makes a variable read-only. Once defined, its value can’t be changed. I use it for values that should remain fixed, like Pi.

15. What are the advantages of C programming language?

C is fast, portable, and reliable. It gives more control over memory. It’s widely used in system programming, operating systems, and embedded systems even in 2025.

Note – C program interview questions for freshers often include basics like variable declarations, loops, functions, and simple output-based problems.

C Language Interview Questions for Experienced

Let’s go through key C programming interview questions with answers, ideal for experienced candidates facing advanced technical rounds.

16. What are function pointers and how are they used?

Function pointers point to functions instead of data. They’re used for callbacks, event-driven code, and menu-driven programs. I’ve used them for implementing plugin-like features in C.

17. Explain memory leaks and how to prevent them.

A memory leak happens when allocated memory isn’t freed. The program keeps using memory, even if it’s not needed anymore. Use free() after malloc() or calloc() to release memory. Tools like Valgrind help find leaks.

18. How does dynamic memory allocation work in C?

In C, dynamic memory is allocated using malloc(), calloc(), or realloc(). Memory is taken from the heap. I always check if the pointer returned is NULL before using it.

19. What is the difference between deep copy and shallow copy?

A shallow copy copies pointer addresses, not actual data. A deep copy copies both values and memory, creating separate instances. I use deep copy when I need true data separation.

20. How do you handle errors in C programs?

I check return values of functions like malloc(), fopen(), or scanf(). If something fails, I print a clear error and exit. Using errno and perror() also helps track system-level errors.

21. How do you manage memory in large-scale C applications to maintain efficiency and prevent leaks?

This is one of the most common C interview questions for 5 years experienced professionals. 

I use memory pools for repeated allocations and always document ownership rules. Every malloc() has a matching free(). I write wrappers for memory tracking and run leak checks regularly. Keeping the code modular and well-documented also helps me trace memory use easily.

Note – C program interview questions for experienced often cover pointers, memory management, file handling, data structures, and optimization techniques.

Advanced C Interview Questions

Here are some challenging C language interview questions designed to test your deep understanding of advanced concepts in C.

22. Explain the concept of volatile variables.

A volatile variable tells the compiler not to optimize it. Its value can change at any time, like when accessed by hardware or interrupts. Without volatile, the compiler might skip re-reading it, assuming it hasn’t changed.

23. How does the inline function work in C?

An inline function suggests that code be inserted directly at the call site. This avoids function call overhead. It’s only a hint—the compiler may ignore it. I use inline for small, frequently called functions.

24. What are the differences between macros and inline functions?

Macros are handled by the preprocessor. They don’t do type checking. Inline functions are type-safe and support debugging. Macros can lead to hard-to-find bugs, so I prefer inline functions where possible.

25. How do you implement dynamic arrays in C?

I use malloc() or calloc() to allocate memory for an array at runtime. To grow it, I use realloc(). I always check for NULL before using the returned pointer and remember to free() the memory.

26. What is the role of the restrict keyword?

The restrict keyword tells the compiler that a pointer is the only reference to that memory block. This allows better optimization. It’s mainly used in performance-critical code. But I use it only when I’m sure no aliasing exists.

Note – C programming language questions for advanced-level include topics like dynamic memory allocation, pointer arithmetic, structures, and compiler-level behavior.

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C Programming Interview Questions

Here are some commonly asked C programming coding questions and answers to help you strengthen your logic and prepare for technical rounds.

27. How do you implement a linked list in C?

To create a linked list, I define a struct with a data field and a pointer to the next node. I then use dynamic memory (malloc) to allocate each node and connect them using pointers. The head node points to the start of the list.

28. How do you handle file operations in C?

I use fopen() to open a file, fprintf() or fread() to write or read, and fclose() to close the file. I always check if the file pointer is NULL before proceeding. Proper error checks prevent crashes.

29. Explain the use of bit fields in structures.

Bit fields allow me to specify the number of bits used for a variable in a struct. I use them when memory size is critical, like in embedded systems or flags. 

Example:

struct status {

  unsigned int error:1;

  unsigned int ready:1;

};

30. How do you manage concurrency in C programs?

I use POSIX threads (pthreads) to run tasks in parallel. For thread safety, I use mutexes or semaphores to avoid race conditions. In real-time or embedded systems, I’m careful with shared data and timing.

Note – C programming questions often test your understanding of logic building, memory handling, recursion, and debugging simple to complex code.

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C Coding Interview Questions

Here are some practical C coding interview questions and answers to test your problem-solving and hands-on programming skills in real scenarios.

31. Write a program to reverse a string (using standard functions).

I take a character array, use two pointers—one at the start, one at the end—and swap characters until they meet. Here’s a short example:

#include <stdio.h>

#include <string.h>

void reverse(char str[]) {

    int i = 0, j = strlen(str) – 1;

    while(i < j) {

        char temp = str[i];

        str[i] = str[j];

        str[j] = temp;

        i++; j–;

    }

}

32. Implement a function to check if a number is a palindrome.

I reverse the number and compare it to the original:

int isPalindrome(int num) {

    int original = num, reversed = 0;

    while(num != 0) {

        reversed = reversed * 10 + num % 10;

        num /= 10;

    }

    return original == reversed;

}

33. Write a program to find the factorial of a number using recursion.

A base case for n == 0, then return n * fact(n – 1).

int factorial(int n) {

    if(n == 0) return 1;

    return n * factorial(n – 1);

}

34. Implement a binary search algorithm.

Binary search splits the array in half and checks mid:

int binarySearch(int arr[], int n, int key) {

    int low = 0, high = n – 1;

    while(low <= high) {

        int mid = (low + high) / 2;

        if(arr[mid] == key) return mid;

        else if(arr[mid] < key) low = mid + 1;

        else high = mid – 1;

    }

    return -1;

}

Note – For C coding questions, always focus on writing clean, error-free code and consider edge cases before finalizing your solution.

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C MCQ Interview Questions

Here are some important C MCQ interview questions to quickly test your theoretical and practical knowledge of the C language.

35. What is the output of the following code snippet?

int a = 5;

printf(“%d”, a++);

a) 6
b) 5
c) Undefined
d) Compiler Error

Answer: b) 5

36. Which of the following is not a valid variable name in C?

a) int number;
b) float rate;
c) int variable_count;
d) int $main;

Answer: d) int $main;

37. What does the sizeof operator return?

a) The length of a variable name
b) The number of bits used by a variable
c) The memory size in bytes of a data type or variable
d) The value stored in a pointer

Answer: c) The memory size in bytes of a data type or variable

38. Which keyword is used to prevent any changes in the variable within a C program?

a) final
b) constant
c) const
d) static

Answer: c) const

39. What is the default return type of functions in C?

a) void
b) float
c) int
d) char

Answer: c) int

Other Important C Interview Questions

This is a list of other important C language interview questions that cover mixed concepts often asked in both written tests and technical interviews.

C Developer Interview Questions

1. How do you handle memory management in C?
2. Explain the concept of modular programming in C.
3. How do you debug a C program?
4. How do you optimize C code for performance?

C and Python Interview Questions

1. Compare memory management in C and Python.
2. How does error handling differ between C and Python?
3. What are the differences in data types between C and Python?
4. How do you interface C code with Python?

C Interview Questions on Pointers

1. What is a null pointer?
2. How do you declare and use a pointer to a function?
3. What are wild pointers and how do they occur?
4. How do you pass a pointer to a function?

C Data Structure Interview Questions

1. How do you implement a stack using arrays?
2. Explain the difference between arrays and linked lists.
3. What is a binary search tree and how is it implemented in C?
4. How do you implement a queue using two stacks?

C String Interview Questions

1. How do you reverse a string in C?
2. What is the difference between strcpy() and strncpy()?
3. How do you compare two strings in C?
4. How do you concatenate two strings in C?

Array Interview Questions in C

1. How do you find the largest element in an array?
2. How do you remove duplicates from an array?
3. How do you merge two sorted arrays?
4. How do you rotate an array by k positions?

C Debugging Interview Questions

1. How do you use gdb to debug a C program?
2. What are common causes of segmentation faults?
3. How do you identify memory leaks in C?
4. How do you handle and log errors in C programs?

C Functions Interview Questions

1. What is the difference between call by value and call by reference?
2. How do you declare and define a function in C?
3. What are inline functions and when should they be used?
4. What is recursion and how is it implemented in C?

Embedded C Interview Questions

1. What is the difference between C and Embedded C?
2. How do you handle interrupts in Embedded C?
3. What is the role of the volatile keyword in Embedded C?
4. What are the challenges in real-time embedded systems programming?

Bit Manipulation in C Interview Questions

1. How do you check if a number is even or odd using bitwise operators?
2. How do you count the number of set bits in an integer?
3. How do you set, clear, and toggle specific bits in a byte?
4. How do you check if a number is a power of two?

Company-Specific C Interview Questions

These are company-specific C programing interview questions commonly asked by top tech firms.

C TCS Interview Questions

Here are some commonly asked C interview questions for TCS to help you prepare for coding and technical rounds.

1. Write a program to find the factorial of a number.
2. Explain the difference between Interpreter and Compiler.
3. What do you understand by enumeration?
4. How do you check for a palindrome string?
5. What is the use of the static keyword in C?

C Programming Interview Questions for Infosys

1. Write a program to check if a number is prime.
2. How do you implement bubble sort?
3. Explain the concept of recursion with an example.
4. How do you find the GCD of two numbers?
5. What is the difference between break and continue statements?

C Programming Interview Questions for Wipro

1. Write a program to find the sum of digits of a number.
2. How do you implement selection sort?
3. Explain the use of pointers in C.
4. How do you handle file operations in C?
5. What is the difference between struct and union?

Note – Wipro embedded C interview questions often focus on bit manipulation, memory optimization, real-time constraints, and hardware-level programming.

Cisco C Interview Questions

1. How do you manage memory in C programs?
2. Explain the concept of function pointers.
3. How do you implement a circular queue?
4. What are the differences between stack and heap memory?
5. How do you prevent buffer overflows?

Google C Interview Questions

1. Implement a function to detect a loop in a linked list.
2. How do you implement quicksort in C?
3. Explain the concept of dynamic memory allocation.
4. How do you handle concurrency in C programs?
5. Write a program to find the nth Fibonacci number.

HCL Embedded C Interview Questions

1. What is the role of the volatile keyword in Embedded C?
2. How do you interface sensors using Embedded C?
3. Explain the concept of ISR (Interrupt Service Routine).
4. How do you manage power consumption in embedded systems?
5. What are the challenges in real-time embedded programming?

L&T Embedded C Interview Questions

1. How do you handle interrupts in Embedded C?
2. Explain the use of timers in embedded systems.
3. How do you implement UART communication in C?
4. What is the difference between polling and interrupt-driven I/O?
5. How do you maintain data integrity in embedded systems?

Zoho Interview Questions in C Programming

1. Write a program to print the Fibonacci series.
2. How do you check if a string is a palindrome?
3. Implement a program to sort an array using insertion sort.
4. How do you find the factorial of a number using recursion?
5. Write a program to count the number of vowels in a string.

Tips to Prepare for C Interview

Preparing for a C interview takes a good understanding of core concepts. Here are some tips to help you.

• Start with basics – data types, loops, arrays, and functions. Be confident in writing clean syntax.
• Practice pointer-related questions daily – they are asked a lot in both coding and theory rounds.
• Learn to write and trace recursive functions step by step.
• Solve common coding problems – string reversal, palindrome check, factorial, and pattern printing.
• Read and write code involving file operations and structures.
• Understand bit manipulation basics – they come up in embedded and low-level rounds.
• Don’t just memorize theory. Code it and test the output.
• Use an online compiler or IDE to debug and improve your coding speed.
• Practice MCQs and time-based coding tests.

Wrapping Up

We hope these C interview questions and answers help you feel more confident during your technical rounds. Interviews can feel tricky, but when you truly understand the logic behind C, things start to click.

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