50 Most Common C Language Interview Questions and Answers

May 20, 2025 admin

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50 Most Common C Language Interview Questions and Answers (With Examples)

C programming is one of the most widely used languages in system-level development and embedded systems. Whether you’re a student, fresher, or an experienced candidate preparing for technical interviews, understanding C thoroughly is essential. Here are 50 of the most frequently asked C language interview questions and answers, explained in detail, complete with real-world examples to make learning effective and memorable.

1. What is C language?

C is a procedural programming language developed in the early 1970s by Dennis Ritchie. It is used for system and application software, embedded firmware, and compilers.

Example:

#include &lt;stdio.h&gt;
int main() {
    printf("Hello, World!\n");
    return 0;
}

#include <stdio.h>

int main() {

printf("Hello, World!\n");

return 0;

}

2. What are the features of C language?

Procedural language
Portable
Low-level access to memory via pointers
Rich set of built-in operators
Modular programming support
Fast and efficient

Example:

#include &lt;stdio.h&gt;
int add(int a, int b) {
    return a + b;
}
int main() {
    printf("%d", add(3, 5));
    return 0;
}

#include <stdio.h>

int add(int a, int b) {

return a + b;

}

int main() {

printf("%d", add(3, 5));

return 0;

}

3. What is the difference between C and C++?

Feature	C	C++
Type	Procedural	Object-Oriented
Encapsulation	Not Supported	Supported via Classes
Function Overloading	Not Supported	Supported
Memory Handling	Manual via malloc/free	Can use new/delete

Example (C):

int sum(int a, int b) {
    return a + b;
}

int sum(int a, int b) {

return a + b;

}

Example (C++):

class Calculator {
public:
    int sum(int a, int b) {
        return a + b;
    }
};

class Calculator {

public:

int sum(int a, int b) {

return a + b;

}

};

4. What is a variable?

A variable is a named location in memory that stores a value. The type of the variable determines what kind of data it can hold.

Example:

int age = 25;
char grade = 'A';
float height = 5.9;

int age = 25;

char grade = 'A';

float height = 5.9;

5. What are data types in C?

There are several fundamental data types in C:

int: for integers
float: for decimal numbers
char: for characters
double: for high-precision decimal numbers
void: represents the absence of a value

Example:

int a = 10;
float b = 10.5;
char c = 'Z';
double d = 10.54321;

int a = 10;

float b = 10.5;

char c = 'Z';

double d = 10.54321;

6. What are operators in C?

Operators perform operations on variables and values. Categories include:

Arithmetic operators (+, -, *, /, %)
Relational operators (==, !=, >, <)
Logical operators (&&, ||, !)
Bitwise operators (&, |, ^, ~)

Example:

int x = 5, y = 10;
printf("Sum: %d", x + y);

int x = 5, y = 10;

printf("Sum: %d", x + y);

7. Explain the use of if-else in C.

if-else is used for decision making. If the condition is true, the if block executes, otherwise else runs.

Example:

int num = 10;
if (num &gt; 0)
    printf("Positive number\n");
else
    printf("Non-positive number\n");

int num = 10;

if (num > 0)

printf("Positive number\n");

else

printf("Non-positive number\n");

8. What is a loop? What are the types?

Loops are used to execute a block of code repeatedly. Types:

for loop
while loop
do-while loop

Example (for loop):

for (int i = 0; i &lt; 5; i++)
    printf("%d ", i);

for (int i = 0; i < 5; i++)

printf("%d ", i);

9. What is the difference between while and do-while loop?

while: condition is checked before execution
do-while: executes at least once regardless of the condition

Example (do-while):

int i = 0;
do {
    printf("%d ", i);
    i++;
} while(i &lt; 3);

int i = 0;

do {

printf("%d ", i);

i++;

} while(i < 3);

10. What is the use of the `break` statement in C?

The break statement is used to exit from loops or switch cases prematurely.

Example:

for (int i = 0; i &lt; 10; i++) {
    if (i == 5) break;
    printf("%d ", i);
}

for (int i = 0; i < 10; i++) {

if (i == 5) break;

printf("%d ", i);

}

11. What is the use of the `continue` statement?

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

Example:

for (int i = 0; i &lt; 5; i++) {
    if (i == 2) continue;
    printf("%d ", i);
}

for (int i = 0; i < 5; i++) {

if (i == 2) continue;

printf("%d ", i);

}

12. What is a function in C?

A function is a block of reusable code that performs a specific task.

Example:

int add(int a, int b) {
    return a + b;
}
int main() {
    printf("%d", add(5, 10));
    return 0;
}

int add(int a, int b) {

return a + b;

}

int main() {

printf("%d", add(5, 10));

return 0;

}

13. What is a pointer?

A pointer is a variable that stores the address of another variable.

Example:

int a = 10;
int *p = &amp;a;
printf("%d", *p); // Outputs: 10

int a = 10;

int *p = &a;

printf("%d", *p); // Outputs: 10

14. How is memory allocated dynamically in C?

Using functions like malloc(), calloc(), realloc(), and free().

Example:

int *arr = (int*) malloc(5 * sizeof(int));
free(arr);

int *arr = (int*) malloc(5 * sizeof(int));

free(arr);

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

malloc() allocates memory without initializing.
calloc() allocates and initializes memory to zero.

Example:

int *a = malloc(5 * sizeof(int));
int *b = calloc(5, sizeof(int));

int *a = malloc(5 * sizeof(int));

int *b = calloc(5, sizeof(int));

16. What is recursion?

Recursion is when a function calls itself.

Example:

int factorial(int n) {
    if (n == 0) return 1;
    else return n * factorial(n - 1);
}

int factorial(int n) {

if (n == 0) return 1;

else return n * factorial(n - 1);

}

17. What is a structure?

A structure is a user-defined data type that groups variables of different types.

Example:

struct Student {
    int id;
    char name[50];
};

struct Student {

int id;

char name[50];

};

18. What is a union?

A union is similar to a structure but shares memory for all its members.

Example:

union Data {
    int i;
    float f;
};

union Data {

int i;

float f;

};

19. What is the difference between structure and union?

In a structure, each member has its own memory.
In a union, all members share the same memory.

Example:

struct Test1 {
    int x;
    float y;
};
union Test2 {
    int x;
    float y;
};

struct Test1 {

int x;

float y;

};

union Test2 {

int x;

float y;

};

20. What are storage classes in C?

They define the scope, visibility, and lifetime of variables. Types:

auto
static
extern
register

Example:

static int count = 0;

1 2	static int count = 0;

21. What is the difference between call by value and call by reference?

In call by value, a copy of the variable is passed to the function. Changes inside the function do not affect the original variable.
In call by reference, the address (pointer) of the variable is passed, so changes inside the function affect the original variable.

Example:

22. What is the purpose of the `sizeof` operator?

The sizeof operator returns the size in bytes of a data type or variable. It helps in memory allocation and understanding system architecture.

Example:

23. What are header files in C?

Header files contain declarations of functions and macros. They are included using the #include directive.

Example:

24. Explain the difference between `struct` and `typedef struct`.

struct defines a structure type.
typedef struct defines a new name (alias) for a structure type, simplifying its usage.

Example:

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25. What is a null pointer?

A pointer that points to nothing (address 0). It is used to signify that the pointer is not currently pointing to any valid memory.

Example:

26. What is pointer arithmetic?

Operations like addition or subtraction done on pointers to traverse memory locations based on the size of the data type pointed to.

Example:

27. What is the difference between `++i` and `i++`?

++i is pre-increment: increments the value before using it.
i++ is post-increment: uses the current value then increments.

Example:

28. What is a dangling pointer?

A pointer that points to memory that has been freed or deallocated. Using it can cause undefined behavior.

Example:

29. What is the difference between `struct` and `class` in C++?

Although not a C concept, in C++,

struct members are public by default.
class members are private by default.

30. What are the different storage classes in C?

auto: default for local variables
static: persists for the program lifetime
extern: external linkage
register: suggests to store variable in CPU register

31. How to declare and use an array in C?

Arrays store multiple elements of the same data type.

Example:

32. What is the difference between an array and a pointer?

An array is a collection of elements stored contiguously, while a pointer holds a memory address. Arrays decay to pointers when passed to functions.

33. What is a constant in C?

A value that cannot be altered during program execution.

34. How do you define a constant?

Using #define or const keyword.

Example:

35. What is the difference between `#include <file>` and `#include "file"`?

<file> searches for the header in standard system directories.
"file" searches in the current directory first.

36. What is the use of the `return` statement in a function?

It returns a value to the caller and ends the function execution.

37. What is recursion? Provide an example.

Recursion is when a function calls itself to solve a problem by breaking it down into smaller subproblems.

Example:

38. What is the difference between `printf` and `scanf`?

printf prints output to the console.
scanf reads input from the user.

39. What is the difference between `++` and `--` operators?

++ increments a variable by 1.
-- decrements a variable by 1.

40. What is an enum in C?

An enum is a user-defined type consisting of named integer constants.

Example:

41. What is a segmentation fault?

An error caused when a program accesses memory that it’s not allowed to.

42. What is the purpose of the `void` keyword?

For functions that return no value.
For pointers to unknown data type (void *).

43. How can you prevent memory leaks in C?

By freeing dynamically allocated memory using free() after use.

44. What is a memory leak?

When allocated memory is not freed, causing wasted memory resources.

45. What is the difference between `fgets` and `gets`?

fgets reads a line with a limit to buffer size (safe).
gets reads input until newline but unsafe and deprecated.

46. What is the difference between `static` and `dynamic` memory allocation?

Static allocation occurs at compile-time (e.g., arrays).
Dynamic allocation occurs at runtime (e.g., malloc).

47. What is a macro?

Macros are preprocessor directives to define reusable code or constants.

Example:

48. How does a `switch` statement work?

It selects code to execute based on the value of an expression.

49. What is the difference between `struct` and `union`?

In a struct, members have separate memory; in a union, members share the same memory location.

50. How do you handle errors in C?

Using error codes, return values, or setting errno and checking it after library calls.

🎯 Final Thoughts

These 50 C language interview questions and answers give you a complete toolkit for cracking interviews confidently. ✨ Keep practicing, test these examples, and review real-world applications to strengthen your foundation.

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50 Most Common C Language Interview Questions and Answers (With Examples)

1. What is C language?

2. What are the features of C language?

3. What is the difference between C and C++?

4. What is a variable?

5. What are data types in C?

6. What are operators in C?

7. Explain the use of if-else in C.

8. What is a loop? What are the types?

9. What is the difference between while and do-while loop?

10. What is the use of the break statement in C?

11. What is the use of the continue statement?

12. What is a function in C?

13. What is a pointer?

14. How is memory allocated dynamically in C?

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

16. What is recursion?

17. What is a structure?

18. What is a union?

19. What is the difference between structure and union?

20. What are storage classes in C?

21. What is the difference between call by value and call by reference?

22. What is the purpose of the sizeof operator?

23. What are header files in C?

24. Explain the difference between struct and typedef struct.

Also Read,

25. What is a null pointer?

26. What is pointer arithmetic?

27. What is the difference between ++i and i++?

28. What is a dangling pointer?

29. What is the difference between struct and class in C++?

30. What are the different storage classes in C?

31. How to declare and use an array in C?

32. What is the difference between an array and a pointer?

33. What is a constant in C?

34. How do you define a constant?

35. What is the difference between #include <file> and #include "file"?

36. What is the use of the return statement in a function?

37. What is recursion? Provide an example.

38. What is the difference between printf and scanf?

39. What is the difference between ++ and -- operators?

40. What is an enum in C?

41. What is a segmentation fault?

42. What is the purpose of the void keyword?

43. How can you prevent memory leaks in C?

44. What is a memory leak?

45. What is the difference between fgets and gets?

46. What is the difference between static and dynamic memory allocation?

47. What is a macro?

48. How does a switch statement work?

49. What is the difference between struct and union?

50. How do you handle errors in C?

🎯 Final Thoughts

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10. What is the use of the `break` statement in C?

11. What is the use of the `continue` statement?

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

22. What is the purpose of the `sizeof` operator?

24. Explain the difference between `struct` and `typedef struct`.

27. What is the difference between `++i` and `i++`?

29. What is the difference between `struct` and `class` in C++?

35. What is the difference between `#include <file>` and `#include "file"`?

36. What is the use of the `return` statement in a function?

38. What is the difference between `printf` and `scanf`?

39. What is the difference between `++` and `--` operators?

42. What is the purpose of the `void` keyword?

45. What is the difference between `fgets` and `gets`?

46. What is the difference between `static` and `dynamic` memory allocation?

48. How does a `switch` statement work?

49. What is the difference between `struct` and `union`?