C Programming Interview Questions and Answers
Last Updated on: 30th Jul 2025 00:07:25 AM
This document provides 20 essential C programming interview questions with concise answers, covering fundamental and advanced topics such as data types, pointers, memory management, functions, and input/output. Designed for interview preparation, the questions use scanf for single-value inputs (integers, floats, characters) and fgets for strings to ensure robust input handling. Each answer is brief, clear, and accurate, making it ideal for quick review.
1. What is the C programming language?
Answer: C is a general-purpose, procedural programming language developed by Dennis Ritchie in 1972, widely used for system programming, embedded systems, and application development due to its efficiency and flexibility.
2. What are the basic data types in C?
Answer: int, float, double, char, void.
3. What is the difference between printf and scanf ?
Answer: printf outputs data to the console; scanf reads user input from the console.
4. What is a pointer in C?
Answer: A pointer is a variable that stores the memory address of another variable.
5. What is the difference between malloc and calloc?
Answer: malloc allocates uninitialized memory; calloc allocates zero-initialized memory.
6. What is a structure in C?
Answer: A structure is a user-defined data type that groups variables of different types under a single name.
7. What is the difference between struct and union?
Answer: struct allocates memory for all members; union allocates memory for the largest member, shared by all.
8. What is the purpose of the static keyword?
Answer: static retains a variable’s value between function calls and restricts its scope to the file or function.
9. What is the difference between while and do-while loops?
Answer: while checks the condition before execution; do-while executes at least once before checking.
10. What is a function in C?
Answer: A function is a reusable block of code that performs a specific task.
11. What is recursion in C?
Answer: Recursion is when a function calls itself to solve a problem.
12. What is the difference between pass by value and pass by reference?
Answer: Pass by value sends a copy of the value; pass by reference sends the memory address.
13. What is a null pointer?
Answer: A null pointer points to no valid memory location (NULL).
14. What is the use of the const keyword?
Answer: const makes a variable’s value unmodifiable after initialization.
15. What is the difference between #include <stdio.h> and #include "stdio.h"?
Answer: <stdio.h> searches standard library paths; "stdio.h" searches the local directory first.
16. What is a macro in C?
Answer: A macro is a preprocessor directive that defines constants or code snippets using #define.
17. What is the purpose of return 0 in the main function?
Answer: It indicates successful program execution to the operating system.
18. What is a dangling pointer?
Answer: A dangling pointer points to memory that has been freed or deallocated.
19. What is the difference between fgets and scanf for string input?
Answer: fgets reads a line safely with buffer control; scanf reads until whitespace and may cause buffer overflow if not used carefully.
20. What is the purpose of the volatile keyword?
Answer: volatile tells the compiler that a variable’s value may change unexpectedly, preventing optimization.
These questions are commonly asked in C programming interviews and cover a wide range of topics