Master C Programming interviews with these structured, detailed questions and answers with examples and images for visual learning, categorized for freshers, intermediate, and experienced candidates preparing for product and service-based company interviews in 2025.
C Programming Interview Questions – For Freshers
1. What is C programming?
C is a general-purpose, procedural programming language used for system and application development due to its simplicity and control over system resources.
2. What are the basic data types in C?
int, char, float, double.
3. What is the use of printf() and scanf()?
printf() is used for output, scanf() is used for input in C programs.
4. Explain the structure of a C program.
Header files, main function, variable declarations, statements, and return statement.
5. What is a pointer in C?
A pointer is a variable that stores the address of another variable.
6. What is the use of a pointer?
To access memory directly, dynamic memory allocation, and efficient array and structure handling.
7. What is the difference between = and == in C?
= is an assignment operator, == is a comparison operator.
8. What is a loop? Name its types.
A loop executes a block repeatedly. Types: for, while, do-while.
9. What is an array in C?
An array is a collection of elements of the same type stored in contiguous memory locations.
10. What is a string in C?
A string is a collection of characters ending with a null character ‘\0’.
11. What is the use of sizeof() operator?
To get the size of a data type or variable in bytes.
12. What is a function in C?
A block of code that performs a specific task and can be reused.
13. What is recursion in C?
A function calling itself to solve a problem.
14. What is the difference between call by value and call by reference?
Call by value passes a copy of the value, call by reference passes the address of the variable.
15. What is a structure in C?
A user-defined data type that groups different data types under a single name.
16. What is a union in C?
A user-defined data type like a structure but with shared memory for all its members.
17. Explain the difference between structure and union.
Structures allocate memory for each member, unions share memory among members.
18. What is a pointer to a pointer in C?
A pointer that stores the address of another pointer.
19. What is dynamic memory allocation?
Allocating memory at runtime using malloc(), calloc(), realloc(), and freeing with free().
20. What is a null pointer?
A pointer initialized with NULL to indicate it is not pointing to any memory location.
C Programming Interview Questions – Intermediate Level
21. What are storage classes in C?
They define the scope, lifetime, and visibility of variables: auto, static, extern, and register.
22. What is the difference between local and global variables?
Local variables are declared inside functions; global variables are declared outside all functions and accessible throughout the program.
23. What is the difference between call by reference and call by value with an example?
Call by value passes a copy of the variable, while call by reference passes the address, allowing modifications.
24. Explain the concept of pointer arithmetic.
Using increment, decrement, addition, and subtraction with pointers to navigate memory addresses.
25. What is a dangling pointer?
A pointer pointing to a memory location that has been freed or deleted.
26. What is the difference between malloc() and calloc()?
malloc() allocates uninitialized memory, calloc() allocates zero-initialized memory.
27. Explain the use of realloc() in C.
It resizes previously allocated memory blocks during runtime.
28. What is a memory leak?
Failure to release memory that is no longer in use, leading to wasted memory.
29. What is the difference between gets() and fgets()?
gets() reads a line without bounds checking (unsafe), while fgets() allows specifying the buffer size (safer).
30. What are command line arguments in C?
Arguments passed to the main() function while executing the program for dynamic input.
31. Explain recursion with an example in C.
Using factorial calculation to illustrate a function calling itself with reduced parameters.
32. What are preprocessor directives?
Commands executed before compilation like #define, #include, #ifdef.
33. What is macro in C?
A fragment of code defined with #define to replace repetitive code.
34. What is the difference between macro and function?
Macros are expanded by the preprocessor without type checking, while functions have type checking and runtime overhead.
35. What is typedef in C?
Used to create new names (aliases) for existing data types to improve code readability.
36. What is the use of const keyword?
Declares variables as constant, preventing modification after initialization.
37. What is volatile keyword in C?
Tells the compiler that the variable may change at any time, preventing optimizations.
38. What is an inline function in C?
A function suggested to be expanded inline to reduce function call overhead.
39. Explain the use of bitwise operators in C.
Used to perform bit-level operations like AND, OR, XOR, NOT, shift operations.
40. How can you implement a linked list in C?
By using structures and pointers to link nodes containing data and address of the next node.
C Programming Interview Questions – For Experienced
41. What is memory management in C?
Efficient allocation, reallocation, and deallocation of memory using malloc, calloc, realloc, and free for optimal resource usage.
42. How do you prevent memory leaks in C?
By ensuring every malloc or calloc has a corresponding free, and careful pointer handling.
43. Explain function pointers in C with an example.
Pointers that point to functions, allowing dynamic function calls and callback implementations.
44. How can you implement a stack using arrays and linked lists in C?
By using array indexing or linked list pointers for push, pop, and peek operations.
45. How do you implement a queue using linked lists?
Using a structure with front and rear pointers, enqueuing at the rear and dequeuing from the front.
46. What are static and dynamic libraries in C?
Static libraries (.lib/.a) are linked at compile time; dynamic libraries (.dll/.so) are linked at runtime.
47. Explain the use of the static keyword with functions.
Limits the scope of functions to the current file for encapsulation.
48. What are file operations in C?
Opening, reading, writing, and closing files using fopen, fread, fwrite, fclose functions.
49. How do you handle errors in file operations?
Using functions like ferror() and feof(), and checking return values of file operations.
50. What are enumerations in C?
User-defined data types consisting of named integer constants for better readability.
51. How to implement dynamic data structures in C?
Using pointers and structures to create linked lists, trees, and graphs dynamically.
52. What is the difference between deep copy and shallow copy in C?
Shallow copy copies addresses (pointers), deep copy duplicates the data in new memory locations.
53. Explain the use of the const keyword with pointers.
To declare constant pointers or pointers to constant data for controlled modification.
54. What is the use of volatile with hardware registers?
Prevents the compiler from optimizing out hardware changes, ensuring actual register values are read.
55. How is endianness handled in C?
By checking the byte order and using bitwise operations to convert between big-endian and little-endian formats.
56. What is the difference between exit() and _exit() in C?
exit() performs cleanup and flushes buffers, _exit() terminates the process immediately without cleanup.
57. How is multi-threading handled in C?
By using pthreads for thread creation, synchronization, and management on supported systems.
58. What is the use of signal handling in C?
To handle asynchronous events using signal() and sigaction() functions.
59. Explain the concept of IPC in C.
Inter-Process Communication (IPC) involves using pipes, message queues, and shared memory for process communication.
60. How do you debug C programs efficiently?
Using tools like GDB, valgrind, and writing test cases for step-by-step debugging and memory analysis.
61. What are the different ways to pass a structure to a function in C?
By passing individual members, by passing the entire structure by value, or by passing a pointer to the structure.
62. Explain the concept of recursion with an example in C.
Recursion is when a function calls itself, for example calculating factorial using factorial(n) = n * factorial(n-1).
63. How do you handle variable argument lists in C?
Using stdarg.h with va_list, va_start, va_arg, and va_end macros.
64. What is a static variable inside a function in C?
It retains its value between function calls and has local scope.
65. Explain the use of the restrict keyword in C99.
Indicates that for the lifetime of the pointer, only it or a value directly derived from it will be used to access the object it points to.
66. What is the purpose of the extern keyword?
To declare a global variable or function in another file.
67. How do you handle memory alignment in C?
Using #pragma pack, compiler-specific attributes, or aligning structures manually for efficient access.
68. What is pointer decay in C?
When an array is passed to a function, it decays into a pointer to its first element.
69. Explain memory segmentation in C.
Memory is divided into segments like text, data, heap, and stack for organized management.
70. What is the difference between stack and heap memory?
Stack is for static memory allocation and function call management, heap is for dynamic memory allocation at runtime.
71. How can you prevent buffer overflows in C?
By performing bounds checking and using safer functions like fgets instead of gets.
72. What is the difference between memcpy() and memmove()?memcpy does not handle overlapping memory areas, while memmove safely handles overlapping regions.
73. How can you implement a circular queue in C?
Using arrays with front and rear pointers that wrap around using modulo operations.
74. What is tail recursion in C?
A recursive function where the recursive call is the last operation, allowing optimization by the compiler.
75. How do you perform bit manipulation in C?
Using bitwise operators like &, |, ^, ~, <<, >> for setting, clearing, toggling, and checking bits.
76. How can you create a multi-dimensional array dynamically in C?
By using pointers to pointers and allocating memory using malloc in nested loops.
77. What are unions used for in embedded systems in C?
To save memory by allowing different data types to share the same memory location.
78. What are inline assembly codes in C?
Assembly instructions embedded within C code using compiler-specific syntax for low-level hardware control.
79. Explain the concept of function inlining and its benefits.
Replacing a function call with the function code itself to reduce overhead and increase speed.
80. How can you measure the execution time of a C program?
Using clock() function in time.h or platform-specific profiling tools.
81. What is a segmentation fault in C?
An error caused by accessing memory that is not allowed.
82. How is dynamic memory managed in embedded C?
By using static allocations or controlled dynamic allocation with proper freeing and low fragmentation.
83. How does the compiler handle const variables?
They may be placed in read-only sections and can be optimized aggressively.
**84. Explain the difference between const char p and char const p.const char *p means the value pointed is constant, char *const p means the pointer itself is constant.
85. What are the different phases of C program compilation?
Preprocessing, Compilation, Assembly, and Linking.
86. What is a memory map in embedded C systems?
A diagram that shows how memory is organized and used in an embedded system.
87. How do you handle concurrency in embedded C?
Using interrupts, critical sections, and RTOS mechanisms.
88. What are critical sections and how are they handled in C?
Sections of code that should not be interrupted, handled by disabling interrupts or using mutexes.
89. Explain volatile with ISR in embedded C.
Variables shared between ISR and main code should be volatile to ensure proper reading.
90. How do you test C code for embedded systems?
Using unit tests, integration tests, and hardware-in-loop testing.
91. How can you optimize C code for performance?
By using efficient algorithms, minimizing memory accesses, loop unrolling, and using compiler optimizations.
92. What is a linker script in embedded C?
Defines memory layout and placement of code/data in embedded systems.
93. How do you handle low-power design in embedded C?
By managing sleep modes, disabling unused peripherals, and efficient coding practices.
94. How is interrupt latency minimized in embedded systems?
By keeping ISRs short and using prioritization.
95. How do you handle hardware registers in embedded C?
Using pointers to specific addresses and volatile qualifiers.
96. What is a watchdog timer in embedded systems?
A timer that resets the system if the software fails to operate correctly.
97. What is memory-mapped I/O?
Using specific addresses to communicate with hardware peripherals.
98. What is a bootloader in embedded systems?
A small program that loads the main application on startup.
99. How do you implement firmware updates in embedded systems?
By using bootloaders and flash memory management.
100. How is debugging done in embedded C?
Using JTAG, serial debug outputs, LEDs, and hardware debuggers for step-by-step analysis.
Frequently Asked Questions
Are these C Programming interview questions useful for freshers?
Yes, this guide covers foundational to advanced questions suitable for freshers, intermediates, and experienced candidates.
What should I focus on for C interviews in 2025?
Pointers, memory management, recursion, embedded C, and practical coding examples.
Are pointers and memory management important in C interviews?
Yes, they are essential for product and service-based interviews, especially in system programming and embedded roles.
How much time is needed to prepare for C Programming interviews?
2-4 weeks of focused preparation with practical coding will help clear most interviews.
Can non-CS graduates clear C Programming interviews?
Yes, with practice in C concepts, data structures, and memory handling, non-CS graduates can confidently clear interviews.