Ultimate C Programming Interview Questions and Answers (With Coding Examples)

💻 Ultimate C Programming Interview Questions and Answers

If you're preparing for an IT job interview that includes C programming, this guide has everything you need. From beginner to advanced, here are the most asked C interview questions with answers and code examples.

🟢 1. Basic C Concepts

Q1. What is C language?

A procedural programming language developed in 1972. Still used for OS, embedded systems, and compilers due to its performance and control.

Q2. Difference between printf() and scanf()

Feature	printf()	scanf()
Function	Output	Input
Address Operator	Not needed	Required (&)

Q3. What is a pointer?

int x = 10;
int *ptr = &x;
printf("%d", *ptr); // Output: 10

Q4. Difference between ++i and i++

int i = 5;
printf("%d", ++i); // 6
printf("%d", i++); // 6 (but i becomes 7)

Q5. malloc() vs calloc()

Function	malloc()	calloc()
Memory	Uninitialized	Initialized to 0
Syntax	malloc(size)	calloc(n, size)

🟡 2. Intermediate Questions

Q6. What is a static variable?

void counter() {
    static int count = 0;
    count++;
    printf("%d ", count);
}

Q7. What is const?

const int x = 10;
x = 20; // Error

Q8. Structure vs Array

Feature	Structure	Array
Data Types	Different	Same
Access	Dot operator	Index

Q9. What is recursion?

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

Q10. Pass by value vs reference

void swap(int *a, int *b) {
    int temp = *a;
    *a = *b;
    *b = temp;
}

🔴 3. Advanced C Questions

Q11. What is a memory leak?

Occurs when dynamically allocated memory is not freed using free().

Q12. What is a function pointer?

int add(int a, int b) { return a + b; }
int (*fp)(int, int) = add;
printf("%d", fp(3, 4));

Q13. What is volatile?

Tells the compiler not to optimize the variable. Used in hardware programming.

Q14. What is typedef?

typedef unsigned int uint;
uint age = 25;

Q15. Use of sizeof()

printf("%lu", sizeof(int));

💻 4. Coding Questions

Q16. Check Prime

int isPrime(int n) {
    if (n <= 1) return 0;
    for (int i = 2; i*i <= n; i++) {
        if (n % i == 0) return 0;
    }
    return 1;
}

Q17. Reverse String

void reverse(char *str) {
    int l = strlen(str);
    for (int i = 0; i < l/2; i++) {
        char t = str[i];
        str[i] = str[l-i-1];
        str[l-i-1] = t;
    }
}

Q18. Largest in Array

int findMax(int arr[], int n) {
    int max = arr[0];
    for (int i = 1; i < n; i++) {
        if (arr[i] > max) max = arr[i];
    }
    return max;
}

Q19. Swap without temp

void swap(int *a, int *b) {
    *a = *a + *b;
    *b = *a - *b;
    *a = *a - *b;
}

Q20. Check Palindrome

int isPalindrome(char *str) {
    int l = strlen(str);
    for (int i = 0; i < l/2; i++) {
        if (str[i] != str[l-i-1]) return 0;
    }
    return 1;
}

✅ 5. Interview Tips

• Revise syntax, pointers, memory management.
• Practice without IDE (use whiteboard).
• Explain logic during interviews clearly.
• Use online judges like HackerRank, LeetCode.
• Prepare with mock interviews or peers.

Bonus: Want to target FAANG? Practice DSA in C and master Linux system calls, GCC, and file I/O!

🚀 All the best! Comment below if you want more practice sets or a downloadable PDF version!