Top 50 C Coding Interview Questions and Answers (2024)

C is the most popular programming language developed by Dennis Ritchie at the Bell Laboratories in 1972 to develop the UNIX operating systems. It is a general-purpose and procedural programming language. It is faster than the languages like Java and Python. C is the most used language in top companies such as LinkedIn, Microsoft, Opera, Meta, and NASA because of its performance. To get into these companies and other software companies, you need to master some important C coding questions to crack their C Online Assessment round and coding interview.

C Coding Interview Questions and Answers

This article on C Coding Interview Questions offers a comprehensive collection of practice questions suitable for both beginners and advanced learners.

List of 50 C Coding Interview Questions and Answer

Here is a list of 50 C coding interview questions and answers:

1. Find the largest number among the three numbers.

C

// C Program to find
// Largest of three numbers
#include <stdio.h>

int main()
{
    int a = 1, b = 2, c = 3;

    // condition for a is greatest
    if (a > b && a > c)
        printf("%d", a);

    // condition for b is greatest
    else if (b > a && b > c)
        printf("%d", b);

    // remaining conditions
    // c is greatest
    else
        printf("%d", c);

    return 0;
}

Output

3

2. Write a Program to check whether a number is prime or not.

C

// C Program for
// Checking value is
// Prime or not
#include <stdio.h>

int main()
{
    int N = 91;
    int flag = 0;

    // Iterate from 2 to N/2
    for (int i = 2; i <= N / 2; i++) {

        // If n is divisible by any number between 2 and
        // n/2, it is not prime
        if (N % i == 0) {
            flag = 1;
            break;
        }
    }

    if (flag == 0)
        printf("Not a Prime Number");
    else
        printf("Is a Prime Number");
    return 0;
}

Output

Is a Prime Number

3. Write a C program to calculate Compound Interest.

C

// C program to calculate Compound Interest
#include <stdio.h>

// For using pow function we must
// include math.h
#include <math.h>

// Driver code
int main()
{
    // Principal amount
    double principal = 2300;

    // Annual rate of interest
    double rate = 7;

    // Time
    double time = 4;

    // Calculating compound Interest
    double amount
        = principal * ((pow((1 + rate / 100), time)));
    double CI = amount - principal;

    printf("Compound Interest is : %lf", CI);
    return 0;
}

Output

Compound Interest is : 714.830823

4. Write a Program in C to Swap the values of two variables without using any extra variable.

C

// C Program to
// Swap two numbers
// No Extra Space
#include <stdio.h>

int main()
{

    int x = 10;
    int y = 20;

    printf("x: %d , y: %d\n", x, y);

    // Code to swap 'x' and 'y'
    x = x + y;
    y = x - y;
    x = x - y;

    printf("x: %d , y: %d\n", x, y);

    return 0;
}

Output

x: 10 , y: 20
x: 20 , y: 10

5. Write a Program to Replace all 0’s with 1’s in a Number.

C

// C Program for
// Replacing 0 to 1
#include <math.h>
#include <stdio.h>

int main()
{
    int N = 102301;

    int ans = 0;
    int i = 0;
    while (N != 0) {
        // Condition to change value
        if (N % 10 == 0)
            ans = ans + 1 * pow(10, i);
        else
            ans = ans + (N % 10) * pow(10, i);

        N = N / 10;
        i++;
    }

    printf("%d", ans);

    return 0;
}

Output:

112311

6. Write a Program to convert the binary number into a decimal number.

C

// C Program for converting
// binary to decimal
#include <stdio.h>

int main()
{
    int N = 11011;

    // Initializing base value a to 1
    int a = 1;
    int ans = 0;
    while (N != 0) {
        ans = ans + (N % 10) * a;
        N = N / 10;
        a = a * 2;
    }

    printf("%d", ans);
    return 0;
}

Output

27

7.  Write a Program to check if the year is a leap year or not.

C

// C Program to check
// Year is leap year or not
#include <stdio.h>

// Function Declaration to check leap year
void leap_year(int year)
{
    // If a year is multiple of 400, then leap year
    if (year % 400 == 0)
        printf("%d is a leap year.\n", year);

    // If a year is multiple of 100, then not a leap year
    else if (year % 100 == 0)
        printf("%d is not a leap year.\n", year);

    // If a year is multiple of 4, then leap year
    else if (year % 4 == 0)
        printf("%d is a leap year.\n", year);

    // Not leap year
    else
        printf("%d is not a leap year.\n", year);
}

int main()
{
    leap_year(2000);
    leap_year(2002);
    leap_year(2008);

    return 0;
}

Output

2000 is a leap year.
2002 is not a leap year.
2008 is a leap year.

8. Write a program to Factorial of a Number.

C

// C Program to calculate
// Factorial of a number
#include <stdio.h>

// Calculating factorial using iteration
void factorial_iteration(int N)
{
    unsigned long long int ans = 1;
    for (int i = 1; i <= N; i++) {
        ans = ans * i;
    }

    printf("Factorial of %d is %lld\n", N, ans);
}

// Calculating factorial using recursion
int factorial(int N)
{
    if (N == 0)
        return 1;

    // Recursive call
    return N * factorial(N - 1);
}

int main()
{
    int n;
    n = 13;
    factorial_iteration(n);

    n = 9;
    printf("Factorial of %d using recursion:%d\n", n,
           factorial(n));

    return 0;
}

Output

Factorial of 13 is 6227020800
Factorial of 9 using recursion:362880

9. Write a Program to Check if a number is an Armstrong number or not.

C

// C program to check if number
// is Armstrong number or not
#include <stdio.h>

// Function to calculate x raised to the power y
int power(int x, unsigned int y)
{
    if (y == 0)
        return 1;
    if (y % 2 == 0)
        return power(x, y / 2) * power(x, y / 2);

    return x * power(x, y / 2) * power(x, y / 2);
}

// Function to calculate order of the number
int order(int n)
{
    int res = 0;
    while (n) {
        res++;
        n = n / 10;
    }
    return res;
}

// Function to check whether the given number is
// Armstrong number or not
int isArmstrong(int x)
{
    // Calling order function
    int n = order(x);
    int temp = x, sum = 0;
    while (temp) {
        int r = temp % 10;
        sum += power(r, n);
        temp = temp / 10;
    }

    // If satisfies Armstrong condition
    if (sum == x)
        return 1;
    else
        return 0;
}

// Driver Program
int main()
{
    int x = 120;
    if (isArmstrong(x) == 1)
        printf("True\n");
    else
        printf("False\n");

    x = 1634;
    if (isArmstrong(x) == 1)
        printf("True\n");
    else
        printf("False\n");

    return 0;
}

Output

False
True

10. Write a program to Find all the roots of a quadratic equation in C.

C

// C program to find roots
// of a quadratic equation
#include <math.h>
#include <stdio.h>
#include <stdlib.h>

// Prints roots of quadratic equation ax*2 + bx + x
void find_roots(int a, int b, int c)
{
    // If a is 0, then equation is not quadratic, but
    // linear
    if (a == 0) {
        printf("Invalid");
        return;
    }

    int d = (b * b) - (4 * a * c);
    double sqrt_val = sqrt(abs(d));

    if (d > 0) {
        printf("Roots are real and different \n");
        printf("%f\n%f", (double)(-b + sqrt_val) / (2 * a),
               (double)(-b - sqrt_val) / (2 * a));
    }
    else if (d == 0) {
        printf("Roots are real and same \n");
        printf("%f", -(double)b / (2 * a));
    }
    else // d < 0
    {
        printf("Roots are complex \n");
        printf("%f + i%f\n%f - i%f", -(double)b / (2 * a),
               sqrt_val / (2 * a), -(double)b / (2 * a),
               sqrt_val / (2 * a));
    }
}

// Driver code
int main()
{
    int a = 1, b = -16, c = 1;

    // Function call
    find_roots(a, b, c);
    return 0;
}

Output:

Roots are real and different
15.937254
0.062746

11. Write a Program to reverse a number.

C

// C Programs to Calculate
// reverse of a number
#include <stdio.h>

// Iterative approach
int reverse_iteration(int N)
{
    int ans = 0;
    while (N != 0) {

        ans = ans * 10 + (N % 10);
        N = N / 10;
    }

    return ans;
}

// recursive approach
int reverse(int n, int ans)
{
    if (n == 0)
        return ans;

    ans = ans * 10 + n % 10;
    return reverse(n / 10, ans);
}

int main()
{
    int N = 15942;
    printf("Initial number:%d\n", N);

    N = reverse_iteration(N);
    printf("%d after reverse using iteration\n", N);

    int ans = 0;
    ans = reverse(N, ans);
    printf("%d after again reverse using recursion", ans);

    return 0;
}

Output

Initial number:15942
24951 after reverse using iteration
15942 after again reverse using recursion

12. Check whether a number is a palindrome.

C

// C Program for
// Checking Palindrome
#include <stdio.h>

// Checking if the number is
// Palindrome number
void check_palindrome(int N)
{
    int T = N;
    int rev = 0; // This variable stored reversed digit

    // Execute a while loop to reverse digits of given
    // number
    while (T != 0) {
        rev = rev * 10 + T % 10;
        T = T / 10;
    }

    // Compare original_number with reversed number
    if (rev == N)
        printf("%d is palindrome\n", N);
    else
        printf("%d is not a palindrome\n", N);
}

int main()
{
    int N = 13431;
    int M = 12345;

    // Function call
    check_palindrome(N);
    check_palindrome(M);

    return 0;
}

Output

13431 is palindrome
12345 is not a palindrome

13. Write a C Program to check if two numbers are equal without using the bitwise operator. 

C

// C Program for checking numbers
// are equal using bitwise operator
#include <stdio.h>

int main()
{
    int x = 1;
    int y = 2;

    // Using XOR
    // XOR of two equal numbers is 0
    if (!(x ^ y))
        printf(" %d is equal to %d ", x, y);
    else
        printf(" %d is not equal to %d ", x, y);

    return 0;
}

Output

 1 is not equal to 2 

14. Write a  C program to find the GCD of two numbers.

C

// C program to find GCD of two numbers
#include <math.h>
#include <stdio.h>

// Function to return gcd of a and b
int gcd(int a, int b)
{
    // Find Minimum of a and b
    int result = ((a < b) ? a : b);
    while (result > 0) {
        if (a % result == 0 && b % result == 0) {
            break;
        }
        result--;
    }
    return result; // return gcd of a and b
}

// Driver program to test above function
int main()
{
    int a = 98, b = 56;
    printf("GCD of %d and %d is %d ", a, b, gcd(a, b));
    return 0;
}

Output

GCD of 98 and 56 is 14 

15. Write a  C program to find the LCM of two numbers.

C

// C program to find
// LCM of two numbers
#include <stdio.h>

// minimum of two numbers
int Min(int Num1, int Num2)
{
    if (Num1 >= Num2)
        return Num2;
    else
        return Num1;
}

int LCM(int Num1, int Num2, int K)
{
    // If either of the two numbers
    // is 1, return their product
    if (Num1 == 1 || Num2 == 1)
        return Num1 * Num2;

    // If both the numbers are equal
    if (Num1 == Num2)
        return Num1;

    // If K is smaller than the
    // minimum of the two numbers
    if (K <= Min(Num1, Num2)) {

        // Checks if both numbers are
        // divisible by K or not
        if (Num1 % K == 0 && Num2 % K == 0) {

            // Recursively call LCM() function
            return K * LCM(Num1 / K, Num2 / K, 2);
        }

        // Otherwise
        else
            return LCM(Num1, Num2, K + 1);
    }

    // If K exceeds minimum
    else
        return Num1 * Num2;
}

int main()
{
    // Given N & M
    int N = 12, M = 9;

    // Function Call
    int ans = LCM(N, M, 2);

    printf("%d", ans);

    return 0;
}

Output

36

16. Write a C Program to find the Maximum and minimum of two numbers without using any loop or condition. 

C

// C Program to check
// Maximum and Minimum
// Between two numbers
// Without any condition or loop
#include <stdio.h>
#include <stdlib.h>

int main()
{
    int a = 55, b = 23;

    // return maximum among the two numbers
    printf("max = %d\n", ((a + b) + abs(a - b)) / 2);

    // return minimum among the two numbers
    printf("min = %d", ((a + b) - abs(a - b)) / 2);

    return 0;
}

Output

max = 55
min = 23

17. Write a Program in C to Print all natural numbers up to N without using a semi-colon.

C

// C program to print
// all natural numbers
// upto N without using semi-colon
#include <stdio.h>
#define N 10

int main(int val)
{
    if (val <= N && printf("%d ", val) && main(val + 1)) {
    }
}

Output

1 2 3 4 5 6 7 8 9 10 

18. Write a Program to find the area of a circle.

C

// C program to find area
// of circle
#include <math.h>
#include <stdio.h>
#define PI 3.142

double findArea(int r) { return PI * pow(r, 2); }

int main()
{
    printf("Area is %f", findArea(5));
    return 0;
}

Output

Area is 78.550000

19.  Write a Program to create a pyramid pattern using C.

C

// C Program print Pyramid pattern
#include <stdio.h>

int main()
{
    int N = 5;

    // Outer Loop for number of rows
    for (int i = 1; i <= N; i++) {

        // inner Loop for space printing
        for (int j = 1; j <= N - i; j++)
            printf(" ");

        // inner Loop for star printing
        for (int j = 1; j < 2 * i; j++)
            printf("*");
        printf("\n");
    }
    return 0;
}

Output

    *
   ***
  *****
 *******
*********

20. Write a program to form Pascal Triangle using numbers.

        1   
      1   1   
    1   2   1   
  1   3   3   1   
1   4   6   4   1

C

// C Program to print
// Pascal's Triangle
#include <stdio.h>

int main()
{
    int n = 5;


    for (int i = 1; i <= n; i++) {
        for (int j = 1; j <= n - i; j++) {
            printf("  ");
        }

        int x = 1;

        for (int j = 1; j <= i; j++) {
            printf("%d   ", x);
            x = x * (i - j) / j;
        }
        printf("\n");
    }

    return 0;
}

Output

        1   
      1   1   
    1   2   1   
  1   3   3   1   
1   4   6   4   1   

21. Write a Program to return the nth row of Pascal’s triangle.

C

// C program to return the Nth row of pascal's triangle
#include <stdio.h>

// Print the N-th row of the Pascal's Triangle
void generateNthrow(int N)
{
    // nC0 = 1
    int prev = 1;
    printf("%d", prev);

    for (int i = 1; i <= N; i++) {
        // nCr = (nCr-1 * (n - r + 1))/r
        int curr = (prev * (N - i + 1)) / i;
        printf(",%d ", curr);
        prev = curr;
    }
}

int main()
{
    int n = 5;
    generateNthrow(n);
    return 0;
}

Output

1,5 ,10 ,10 ,5 ,1 

22. Write a program to reverse an Array.

C

// C Program to reverse
// An array
#include <stdio.h>

void reverse(int* arr, int n)
{
    // Swapping front and back elements.
    for (int i = 0, j = n - 1; i < j; i++, j--) {
        int ele = arr[i];
        arr[i] = arr[j];
        arr[j] = ele;
    }
}

int main()
{

    int arr[] = { 1, 2, 3, 4, 5 };
    // Function Call
    reverse(arr, 5);

    // reverse array element printing
    for (int i = 0; i < 5; i++)
        printf("%d ", arr[i]);

    return 0;
}

Output

5 4 3 2 1 

23. Write a program to check the repeating elements in C.

C

// C Program for
// checking duplicate
// values in a array
#include <stdio.h>

int Sort(int arr[], int size)
{
    for (int i = 0; i < size - 1; i++) {

        for (int j = 0; j < size - i - 1; j++) {
            if (arr[j] > arr[j + 1]) {
                int temp = arr[j];
                arr[j] = arr[j + 1];
                arr[j + 1] = temp;
            }
        }
    }
}

// find repeating element
void findRepeating(int arr[], int n)
{
    int count = 0;
    for (int i = 0; i < n; i++) {

        int flag = 0;
        while (i < n - 1 && arr[i] == arr[i + 1]) {
            flag = 1;
            i++;
        }
        if (flag)
            printf("%d ", (arr[i - 1]));
    }

    return;
}

int main()
{
    int arr[] = { 1, 3, 4, 1, 2, 3, 5, 5 };

    int n = sizeof(arr) / sizeof(arr[0]);

      Sort(arr,n);

      findRepeating(arr,n);



    return 0;
}

Output

1 3 5 

24. Write a Program to print the Maximum and Minimum elements in an array.

C

// C Program for calculating
// maximum and minimum element
#include <stdio.h>

void find_small_large(int arr[], int n)
{
    int min, max;

    // assign first element as minimum and maximum
    min = arr[0];
    max = arr[0];

    for (int i = 1; i < n; i++) {

        // finding smallest here
        if (arr[i] < min)
            min = arr[i]; // finding largest here
        if (arr[i] > max)
            max = arr[i];
    }
    printf("Maximum: %d and Minimum: %d\n", min, max);
}

int main()
{
    int arr[] = { 15, 14, 35, 2, 11, 83 };
    int len = sizeof(arr) / sizeof(arr[0]);

    // Function call
    find_small_large(arr, len);

    return 0;
}

Output

Smallest: 2 and Largest: 83

25. Write a Program for the cyclic rotation of an array to k positions.

C

// C program to rotate
// Array by  k elements
#include <stdio.h>

// Print array
void printArray(int arr[], int n)
{
    int i;
    for (i = 0; i < n; i++)
        printf("%d ", arr[i]);
}

// Caculates greatest common divisor
int gcd(int a, int b)
{
    if (b == 0)
        return a;
    else
        return gcd(b, a % b);
}

// Rotate array
void Rotate(int arr[], int k, int N)
{
    int i, j, a, temp;
    k = k % N;

    int rotate = gcd(k, N);

    for (i = 0; i < rotate; i++) {

        temp = arr[i];
        j = i;
        while (1) {
            a = j + k;
            if (a >= N)
                a = a - N;
            if (a == i)
                break;
            arr[j] = arr[a];
            j = a;
        }
        arr[j] = temp;
    }
}

int main()
{
    int arr[] = { 1, 2, 3, 4, 5 };

    // Rotating array
    Rotate(arr, 2, 5);

    // Printing array
    printArray(arr, 5);

    return 0;
}

Output

3 4 5 1 2 

26. Write a Program to sort First half in Ascending order and the Second in Descending order.

C

// C Program for Sorting
// First half in Ascending order
// and Second Descending order
#include <stdio.h>

void Sort_asc_desc(int arr[], int n)
{
    int temp;
    for (int i = 0; i < n - 1; i++) {
        for (int j = i + 1; j < n; j++) {
            if (arr[i] > arr[j]) {
                temp = arr[i];
                arr[i] = arr[j];
                arr[j] = temp;
            }
        }
    }

    // printing first half in ascending order
    for (int i = 0; i < n / 2; i++)
        printf("%d ", arr[i]);

    // printing second half in descending order
    for (int j = n - 1; j >= n / 2; j--)
        printf("%d ", arr[j]);
}

int main()
{
    int arr[] = { 11, 23, 42, 16, 83, 73, 59 };
    int N = sizeof(arr) / sizeof(arr[0]);

    Sort_asc_desc(arr, N);

    return 0;
}

Output

11 16 23 83 73 59 42 

27. Write a Program to print sums of all subsets in an array.

C

// C Program to print sum of
// all subsets
#include <stdio.h>

// Function to print sum of subset
// Using recursion
void subset_sum(int arr[], int i, int j, int sum)
{
    if (i > j) {
        printf("%d ", sum);
        return;
    }

    subset_sum(arr, i + 1, j, sum + arr[i]);
    subset_sum(arr, i + 1, j, sum);
}

// driver code
int main()
{
    int arr[] = { 1, 2, 3 };
    int n = sizeof(arr) / sizeof(arr[0]);

    // Function calling to print subset sum
    subset_sum(arr, 0, n - 1, 0);
    return 0;
}

Output

6 3 4 1 5 2 3 0 

28. Write a Program to Find if there is any subarray with a sum equal to 0.

C

// C Program to check 0 sum
// subarray possible
#include <stdio.h>

int main()
{
    // array
    int arr[] = { -2, 2, 1, 1, 8 };
    int n = sizeof(arr) / sizeof(arr[0]);

    int flag = 0, sum;

    // Traversing array to check
    for (int i = 0; i < n; i++) {

        for (int j = i; j < n; j++) {
            sum += arr[j];

            if (sum == 0) {
                flag = 1;
                printf(
                    "True subarray with 0 sum is possible");
                break;
            }
        }
    }

    if (flag == 0)
        printf("No such condition");
}

Output

True subarray with 0 sum is possible

29. Write a C program to Implement Kadane’s Algorithm

C

// C program to implement Kadane's Algorithm
#include <limits.h>
#include <stdio.h>

int main()
{
    int a[] = { -2, -3, 4, -1, -2, 1, 5, -3 };
    int n = sizeof(a) / sizeof(a[0]);

    int max_so_far = INT_MIN, max_ending_here = 0,
        start = 0, end = 0, s = 0;

    for (int i = 0; i < n; i++) {
        max_ending_here += a[i];

        if (max_so_far < max_ending_here) {
            max_so_far = max_ending_here;
            start = s;
            end = i;
        }

        if (max_ending_here < 0) {
            max_ending_here = 0;
            s = i + 1;
        }
    }
    printf("Maximum contiguous sum is %d\n", max_so_far);
    printf("Starting index %d Ending index %d", start, end);

    return 0;
}

Output

Maximum contiguous sum is 7
Starting index 2 Ending index 6

30. Write a Program to find the transpose of a matrix.

C

#include <stdio.h>

// This function stores transpose of A[][] in B[][]
void transpose(int N, int M, int A[M][N], int B[N][M])
{
    int i, j;
    for (i = 0; i < N; i++)
        for (j = 0; j < M; j++)
            B[i][j] = A[j][i];
}

int main()
{
    int M = 3;
    int N = 4;

    int A[3][4] = { { 1, 1, 1, 1 },
                    { 2, 2, 2, 2 },
                    { 3, 3, 3, 3 } };

    // Note dimensions of B[][]
    int B[N][M], i, j;

    transpose(N, M, A, B);

    printf("Result matrix is \n");
    for (i = 0; i < N; i++) {
        for (j = 0; j < M; j++)
            printf("%d ", B[i][j]);
        printf("\n");
    }

    return 0;
}

Output

Result matrix is 
1 2 3 
1 2 3 
1 2 3 
1 2 3 

31. Write a Program to Rotate a matrix by 90 degrees in the clockwise direction in C.

C

// C Program to rotate the array
// By 90 degree in clockwise direction
#include <stdio.h>

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

int main()
{

    int n = 4;
    int arr[4][4] = { { 1, 2, 3, 4 },
                      { 5, 6, 7, 8 },
                      { 9, 10, 11, 12 },
                      { 13, 14, 15, 16 } };

    // Print Orignal Matrix
    printf("Orignal Matrix:\n");
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < n; j++) {
            printf("%d ", arr[i][j]);
        }
        printf("\n");
    }

    // Rotate the matrix about the main diagonal
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < i; j++)
            swap(&arr[i][j], &arr[j][i]);
    }

    // Rotate the matrix about middle column
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < n / 2; j++) {
            swap(&arr[i][j], &arr[i][n - j - 1]);
        }
    }

    // Print the rotated matrix
    printf("Matrix after rotation: \n");
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < n; j++) {
            printf("%d ", arr[i][j]);
        }
        printf("\n");
    }
}

Output

Orignal Matrix:
1 2 3 4 
5 6 7 8 
9 10 11 12 
13 14 15 16 
Matrix after rotation: 
13 9 5 1 
14 10 6 2 
15 11 7 3 
16 12 8 4 

32. Write a Program to find the Spiral Traversal of a Matrix in C.

C

// C Program to find Spiral Traversal
// Of a matrix
#include <stdio.h>

int main()
{
    int arr[4][4] = { { 1, 5, 9, 13 },
                      { 2, 6, 10, 14 },
                      { 3, 7, 11, 15 },
                      { 4, 8, 12, 16 } };

    int m = 4, n = 4;
    int i, l = 0, right = m - 1, begin = 0, end = n - 1;

    while (l <= right && begin <= end) {

        // Print the first row
        // from the remaining rows
        for (i = l; i <= right; ++i) {
            printf("%d ", arr[begin][i]);
        }
        begin++;

        // Print the last column
        // from the remaining columns
        for (i = begin; i <= end; ++i) {
            printf("%d ", arr[i][right]);
        }
        right--;

        // Print the last row from
        // the remaining rows
        if (begin <= end) {
            for (i = right; i >= l; --i) {
                printf("%d ", arr[end][i]);
            }
            end--;
        }

        // Print the first column from
        // the remaining columns
        if (l <= right) {
            for (i = end; i >= begin; --i) {
                printf("%d ", arr[i][l]);
            }
            l++;
        }
    }

    return 0;
}

Output

1 5 9 13 14 15 16 12 8 4 3 2 6 10 11 7 

33. Write a program to count the sum of numbers in a string.

C

#include <stdio.h>

int main()
{

    char s[] = "124259";

    int ans = 0;
    // iterate through all the number
    for (int i = 0; s[i] != '\0'; i++) {
        int ele = s[i] - 48;
        if (ele <= 9)
            ans += ele;
    }

    // print sum of the numbers
    printf("%d", ans);

    return 0;
}

Output

23

34. Program to calculate the length of the string.

C

// C Program to calculate
// length of a string
#include <stdio.h>
#include <string.h>

int length(char s[], int i)
{
    if (s[i] == '\0')
        return 0;

    return length(s, i + 1) + 1;
}

int main()
{
    char s[] = "GeeksforGeeks";

    // Calculating using strlen
    int len = strlen(s);
    printf("length using strlen:%d\n", len);

    // Calculating using iteration
    int i;
    for (i = 0; s[i] != '\0'; i++) {
        continue;
    }
    printf("length using iteration:%d\n", i);

    // Calculating using recursion
    int ans = length(s, 0);
    printf("length using recursion:%d\n", ans);
    return 0;
}

Output

length using strlen:13
length using iteration:13
length using recursion:13

35. Write a program to check string is a palindrome.

C

// C implementation to check if a given
// string is palindrome or not
#include <stdio.h>
#include <string.h>
#include <stdbool.h>

bool is_palindrome(char* str, int i, int j)
{
    if (i >= j) {
        return true;
    }
    if (str[i] != str[j]) {
        return false;
    }
    return is_palindrome(str, i + 1, j - 1);
}

void check_palindrome(char* str)
{

    // Start from leftmost and
    // rightmost corners of str
    int h = 0;
    int flag = 0;
    int l = strlen(str) - 1;

    // Keep comparing characters
    // while they are same
    while (h > l) {
        if (str[l++] != str[h--]) {
            printf("%s is not a palindrome\n", str);
            flag = 1;
            break;
            // will break from here
        }
    }

    if (flag == 0)
        printf("%s is a palindrome\n", str);
}

int main()
{
    char str[] = { "GeekeeG" };
    char str2[] = { "GeeksforGeeks" };

    check_palindrome(str);

    printf("Checking %s using recursive approach\n", str2);
    bool ans = is_palindrome(str2,0,strlen(str2)-1);
    if (ans)
        printf("It is Palindrome\n");
    else
        printf("Not a Palindrome\n");

    return 0;
}

Output

GeekeeG is a palindrome
Checking GeeksforGeeks using recursive approach
Not a Palindrome

36. Write a program to print all permutations of a given string in lexicographically sorted order in C.

C

// C Program to print all permutations of a string in sorted
// order.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

// function two compare two characters a and b
int compare(const void* a, const void* b)
{
    return (*(char*)a - *(char*)b);
}

// function two swap two characters a and b
void swap(char* a, char* b)
{
    char t = *a;
    *a = *b;
    *b = t;
}

// function finds the index of the smallest character
int findCeil(char str[], char first, int l, int h)
{
    int ceilIndex = l;

    for (int i = l + 1; i <= h; i++)
        if (str[i] > first && str[i] < str[ceilIndex])
            ceilIndex = i;

    return ceilIndex;
}

// Print all permutations of str in sorted order
void sortedPermutations(char str[])
{
    int size = strlen(str);

    qsort(str, size, sizeof(str[0]), compare);

    int isFinished = 0;
    while (!isFinished) {
        printf("%s \n", str);

        int i;
        for (i = size - 2; i >= 0; --i)
            if (str[i] < str[i + 1])
                break;

        if (i == -1)
            isFinished = 1;
        else {

            int ceilIndex
                = findCeil(str, str[i], i + 1, size - 1);
            swap(&str[i], &str[ceilIndex]);
            qsort(str + i + 1, size - i - 1, sizeof(str[0]),
                  compare);
        }
    }
}

int main()
{
    char str[] = "123";
    sortedPermutations(str);
    return 0;
}

Output

123 
132 
213 
231 
312 
321 

37. Write a program to calculate the Power of a Number using Recursion in C.

C

// C program  to calculate the Power of a Number using
// Recursion
#include <stdio.h>

int power(int a, int b)
{
    if (b == 0)
        return 1;

    return power(a, b - 1) * a;
}

int main()
{
    int a = 4, b = 5;

    int ans = power(a, b);

    printf("%d", ans);
    return 0;
}

Output

1024

38. Write a Code to print the Fibonacci series using recursion.

C

// C Program to illustrate
// Fibonacci Series using Recursion
#include <stdio.h>

int fibonacci(int n)
{
    if (n <= 1)
        return n;
    return fibonacci(n - 1) + fibonacci(n - 2);
}

int fibonacci_iteration(int n)
{
    if (n <= 1)
        return 1;

    int arr[n + 1];
    arr[0] = 1;
    arr[1] = 1;

    for (int i = 2; i < n + 1; i++)
        arr[i] = arr[i - 1] + arr[i - 2];

    return arr[n];
}

int main()
{
    int n = 9;
    printf("Fibonacci using recursion of %d:%d\n", n,
           fibonacci(n));

    n = 11;
    printf("Fibonacci using iteration of %d:%d", n,
           fibonacci_iteration(n));
    return 0;
}

Output

Fibonacci using recursion of 9:34
Fibonacci using iteration of 11:144

39. Write a Program to find the HCF of two Numbers using Recursion.

C

// C program to find
// GCD of two numbers
#include <stdio.h>

// Recursive function to
// Calculate and return gcd of a and b
int gcd(int a, int b)
{
    // Everything divides 0
    if (a == 0)
        return b;
    if (b == 0)
        return a;

    // base case
    if (a == b)
        return a;

    // a is greater
    if (a > b)
        return gcd(a - b, b);
    return gcd(a, b - a);
}

int main()
{
    int a = 192, b = 36;
    printf("GCD of %d and %d is %d ", a, b, gcd(a, b));
    return 0;
}

Output

GCD of 192 and 36 is 12 

40. Write a Program in C to reverse a string using recursion.

C

// C program to reverse
// String using recursion
#include <stdio.h>
#include <string.h>

// Using Iteration for reverse
void reverse_iteration(char* str)
{
    int i = 0;
    int j = strlen(str) - 1;

    for (; i < j; i++, j--) {
        char temp = str[i];
        str[i] = str[j];
        str[j] = temp;
    }
}

// Using recursion for reverse
void reverse(char* str)
{
    if (*str) {
        reverse(str + 1);
        printf("%c", *str);
    }
}

int main()
{
    char a[] = "Geeks for Geeks";
    printf("Orignal string:%s\n", a);

    reverse_iteration(a);
    printf("Reverse the string(iteration):%s\n", a);

    printf("Using recursion for reverse:");
    reverse(a);

    return 0;
}

Output

Orignal string:Geeks for Geeks
Reverse the string(iteration):skeeG rof skeeG
Using recursion for reverse:Geeks for Geeks

41.  Write a C Program to search elements in an array.

C

// C code to Search elements in array
#include <stdio.h>

int search(int arr[], int N, int x)
{
    int i;

    // iterate through all the element of array
    for (i = 0; i < N; i++)
        if (arr[i] == x)
            return i;
    return -1;
}

int main(void)
{
    int arr[] = { 9, 3, 2, 1, 10, 4 };
    int x = 10;
    int N = sizeof(arr) / sizeof(arr[0]);

    // Function Call
    int result = search(arr, N, x);

    if (result == -1) {
        printf("Element is not present in array");
    }
    else {
        printf("Element is present at index %d", result);
    }

    return 0;
}

Output

Element is present at index 4

42.  Write a C Program to search elements in an array using Binary Search.

C

// C program to Search element
// in Array using Binary Search
#include <stdio.h>

int binarySearch(int arr[], int l, int r, int x)
{
    if (r >= l) {
        int mid = l + (r - l) / 2;

        // If the element is present at the middle
        // itself
        if (arr[mid] == x)
            return mid;

        // If element is smaller than mid, then
        // it can only be present in left subarray
        if (arr[mid] > x)
            return binarySearch(arr, l, mid - 1, x);

        // Else the element can only be present
        // in right subarray
        return binarySearch(arr, mid + 1, r, x);
    }

    return -1;
}

int main()
{
    int arr[] = { 11, 14, 19, 23, 40 };
    int n = sizeof(arr) / sizeof(arr[0]);
    int x = 40;
    int result = binarySearch(arr, 0, n - 1, x);
    if (result == -1) {
        printf("Element is not present in array");
    }
    else {
        printf("Element is present at index %d", result);
    }
    return 0;
}

Output

Element is present at index 4

43. Write a C Program to sort arrays using Bubble, Selection, and Insertion Sort.

C

// C Program to implement
// Sorting Algorithms
#include <stdio.h>

// A function to implement bubble sort
void bubble_sort(int* arr, int n)
{
    for (int j = 0; j < n - 1; j++) {

        // Last j elements are already in place
        for (int i = 0; i < n - j - 1; i++) {
            if (arr[i] > arr[i + 1]) {
                int temp = arr[i];
                arr[i] = arr[i + 1];
                arr[i + 1] = temp;
            }
        }
    }
}

// A function to implement swaping
void swap(int* xp, int* yp)
{
    int temp = *xp;
    *xp = *yp;
    *yp = temp;
}

// A function to implement selectionSort
void selectionSort(int arr[], int n)
{

    // One by one move boundary of unsorted subarray
    for (int i = 0; i < n - 1; i++) {
        // Find the minimum element in unsorted array
        int min_idx = i;
        for (int j = i + 1; j < n; j++)
            if (arr[j] < arr[min_idx])
                min_idx = j;

        // Swap the found minimum element
        // with the first element
        if (min_idx != i)
            swap(&arr[min_idx], &arr[i]);
    }
}

void insertionSort(int arr[], int n)
{

    for (int i = 1; i < n; i++) {
        int key = arr[i];
        int j = i - 1;

        // Move elements of arr that are
        // greater than key, to one position ahead
        // of their current position
        while (j >= 0 && arr[j] > key) {
            arr[j + 1] = arr[j];
            j = j - 1;
        }
        arr[j + 1] = key;
    }
}

int main()
{
    int arr1[] = { 9, 4, 3, 11, 1, 5 };
    int arr2[] = { 4, 3, 9, 1, 5, 11 };
    int arr3[] = { 5, 1, 11, 3, 4, 9 };
    int n = 6;

    printf("Non-Sorted array: ");
    for (int i = 0; i < n; i++)
        printf("%d ", arr1[i]);
    printf("\n");

    // sort array
    bubble_sort(arr1, n);

    // printing array
    printf("Sorted array using Bubble sort: ");
    for (int i = 0; i < n; i++)
        printf("%d ", arr1[i]);
    printf("\n");

    printf("Non-Sorted array: ");
    for (int i = 0; i < n; i++)
        printf("%d ", arr2[i]);
    printf("\n");

    // sort array
    insertionSort(arr2, n);

    // printing array
    printf("Sorted array using Insertion Sort: ");
    for (int i = 0; i < n; i++)
        printf("%d ", arr2[i]);
    printf("\n");

    printf("Non-Sorted array: ");
    for (int i = 0; i < n; i++)
        printf("%d ", arr3[i]);
    printf("\n");

    // sort array
    selectionSort(arr3, n);

    // printing array
    printf("Sorted array using Selection Sort: ");
    for (int i = 0; i < n; i++)
        printf("%d ", arr3[i]);
    printf("\n");

    return 0;
}

Output

Non-Sorted array: 9 4 3 11 1 5 
Sorted array using Bubble sort: 1 3 4 5 9 11 
Non-Sorted array: 4 3 9 1 5 11 
Sorted array using Insertion Sort: 1 3 4 5 9 11 
Non-Sorted array: 5 1 11 3 4 9 
Sorted array using Selection Sort: 1 3 4 5 9 11 

44. Write a C Program to sort arrays using Merge Sort.

C

// C program for
// Sorting array
// using Merge Sort
#include <stdio.h>

void merge(int arr[], int l, int m, int r)
{
    int i, j, k;
    int n1 = m - l + 1;
    int n2 = r - m;

    // create temperary arrays
    int L[n1], R[n2];

    // Copy data to arrays from L[] and R[]
    for (i = 0; i < n1; i++)
        L[i] = arr[l + i];
    for (j = 0; j < n2; j++)
        R[j] = arr[m + 1 + j];

    // Initial index of first ,second
    // and merged subarray respectively
    i = 0;
    j = 0;
    k = l;
    while (i < n1 && j < n2) {
        if (L[i] <= R[j]) {
            arr[k] = L[i];
            i++;
        }
        else {
            arr[k] = R[j];
            j++;
        }
        k++;
    }

    // Copy the remaining elements of L[]
    while (i < n1) {
        arr[k] = L[i];
        i++;
        k++;
    }

    // Copy the remaining elements of R[]
    while (j < n2) {
        arr[k] = R[j];
        j++;
        k++;
    }
}

void mergeSort(int arr[], int l, int r)
{
    if (l < r) {

        // calculating middle term
        int mid = l + (r - l) / 2;

        // divide to sort both halves
        mergeSort(arr, l, mid);
        mergeSort(arr, mid + 1, r);

        merge(arr, l, mid, r);
    }
}

int main()
{
    int arr[] = { 23, 9, 13, 15, 6, 7 };
    int n = sizeof(arr) / sizeof(arr[0]);

    // Printing orignal array
    printf("Given array:");
    for (int i = 0; i < n; i++)
        printf("%d ", arr[i]);
    printf("\n");

    mergeSort(arr, 0, n - 1);

    // Printing sorted array
    printf("Sorted array :");
    for (int i = 0; i < n; i++)
        printf("%d ", arr[i]);
    printf("\n");

    return 0;
}

Output

Given array:23 9 13 15 6 7 
Sorted array :6 7 9 13 15 23 

45. Write a C Program to sort arrays using Quick Sort.

C

// C Program for
// sorting array using
// Quick sort
#include <stdio.h>

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

int partition(int array[], int low, int high)
{
    int pivot = array[high];

    int i = (low - 1);

    // compare elements with the pivot
    for (int j = low; j < high; j++) {
        if (array[j] <= pivot) {
            i++;
            swap(&array[i], &array[j]);
        }
    }

    // swap the pivot element with the greater element at i
    swap(&array[i + 1], &array[high]);

    return (i + 1);
}

void quickSort(int array[], int low, int high)
{
    if (low < high) {
        int pi = partition(array, low, high);
        quickSort(array, low, pi - 1);
        quickSort(array, pi + 1, high);
    }
}

void printArray(int array[], int n)
{
    for (int i = 0; i < n; ++i) {
        printf("%d  ", array[i]);
    }
    printf("\n");
}

int main()
{
    int arr[] = { 28, 7, 20, 1, 10, 3 , 6 };

    int n = sizeof(arr) / sizeof(arr[0]);

    printf("Unsorted Array:");
    printArray(arr, n);

    quickSort(arr, 0, n - 1);

    printf("Sorted array :");
    printArray(arr, n);

    return 0;
}

Output

Unsorted Array:28  7  20  1  10  3  6  
Sorted array :1  3  6  7  10  20  28  

46. Write a program to sort an array using pointers.

C

// C Program to implement
// sorting using pointers
#include <stdio.h>

// Function to sort the numbers using pointers
void sort(int n, int* ptr)
{
    int i, j;

    // Sort the numbers using pointers
    for (i = 0; i < n; i++) {

        for (j = i + 1; j < n; j++) {

            if (*(ptr + j) < *(ptr + i)) {

                int temp = *(ptr + i);
                *(ptr + i) = *(ptr + j);
                *(ptr + j) = temp;
            }
        }
    }

    // print the numbers
    for (i = 0; i < n; i++)
        printf("%d ", *(ptr + i));
}

// Driver code
int main()
{
    int n = 5;
    int arr[] = { 13, 22, 7, 12, 4 };

    sort(n, arr);

    return 0;
}

Output

4 7 12 13 22 

47. Write a C program to Store Information about Students Using Structure

C

// C Program to Store
// Information about Students
// Using Structure
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

// Create the student structure
struct Student {
    char* name;
    int roll_number;
    int age;
};

// Driver code
int main()
{
    int n = 3;

    // Create the student's structure variable
    // with n Student's records
    struct Student student[n];

    // Get the students data
    student[0].roll_number = 1;
    student[0].name = "Geeks1";
    student[0].age = 10;

    student[1].roll_number = 2;
    student[1].name = "Geeks2";
    student[1].age = 11;

    student[2].roll_number = 3;
    student[2].name = "Geeks3";
    student[2].age = 13;

    // Printing  the Structers
    printf("Student Records:\n\n");
    for (int i = 0; i < n; i++) {
        printf("\tName : %s", student[i].name);
        printf("\tRoll Number : %d",
               student[i].roll_number);
        printf("\tAge : %d\n", student[i].age);
    }

    return 0;
}

Output

Student Records:

    Name : Geeks1    Roll Number : 1    Age : 10
    Name : Geeks2    Roll Number : 2    Age : 11
    Name : Geeks3    Roll Number : 3    Age : 13

48.  Write a C Program To Add Two Complex Numbers Using Structures And Functions.

C

// C program to demonstrate
// addition of complex numbers
#include <stdio.h>

// define a structure for complex number
typedef struct complexNumber {
    int real;
    int img;
} complex;


complex add(complex x, complex y)
{
    // define a new complex number.
    complex add;

    // add similar type together
    add.real = x.real + y.real;
    add.img = x.img + y.img;

    return (add);
}

int main()
{

    // define three complex type numbers
    complex x, y, sum;

    // first complex number
    x.real = 4;
    x.img = 5;

    // second complex number
    y.real = 7;
    y.img = 11;

    // printing both complex numbers
    printf(" x = %d + %di\n", x.real, x.img);
    printf(" y = %d + %di\n", y.real, y.img);

    // call add(a,b) function and
    // pass complex numbers a & b
    // as an parameter.
    sum = add(x, y);

    // print result
    printf("\n sum = %d + %di", sum.real, sum.img);

    return 0;
}

Output

 x = 4 + 5i
 y = 7 + 11i

 sum = 11 + 16i

49. Write a C Program to add Two Distance Given as Input in Feet and Inches

C

// C program for calculating sum of
// Distance in intches and feet
#include "stdio.h"

// Struct defined for the inch-feet system
struct InchFeet {
    int feet;
    float inch;
};

// Function to find the sum of all N
// set of Inch Feet distances
void findSum(struct InchFeet arr[], int N)
{

    // Variable to store sum
    int feet_sum = 0;
    float inch_sum = 0.0;

    int x;

    // Traverse the InchFeet array
    for (int i = 0; i < N; i++) {

        // Find the total sum of
        // feet and inch
        feet_sum += arr[i].feet;
        inch_sum += arr[i].inch;
    }

    // If inch sum is greater than 11
    // convert it into feet
    // as 1 feet = 12 inch
    if (inch_sum >= 12) {

        // Find integral part of inch_sum
        x = (int)inch_sum;

        // Delete the integral part x
        inch_sum -= x;

        // Add x%12 to inch_sum
        inch_sum += x % 12;

        // Add x/12 to feet_sum
        feet_sum += x / 12;
    }

    // Print the corresponding sum of
    // feet_sum and inch_sum
    printf("Feet Sum: %d\n", feet_sum);
    printf("Inch Sum: %.2f", inch_sum);
}

int main()
{
    struct InchFeet arr[]
        = { { 11, 5.1 }, { 13, 4.5 }, { 6, 8.1 } };

    int N = sizeof(arr) / sizeof(arr[0]);

    findSum(arr, N);

    return 0;
}

Output

Feet Sum: 31
Inch Sum: 5.70

50. Write a C program to reverse a linked list iteratively

C

// C program to reverse a linked list iteratively
#include <stdio.h>
#include <stdlib.h>

/* Link list node */
struct Node {
    int data;
    struct Node* next;
};

/* Function to reverse the linked list */
static void reverse(struct Node** head_ref)
{
    struct Node* prev = NULL;
    struct Node* current = *head_ref;
    struct Node* next = NULL;
    while (current != NULL) {
        // Store next
        next = current->next;

        // Reverse current node's pointer
        current->next = prev;

        // Move pointers one position ahead.
        prev = current;
        current = next;
    }
    *head_ref = prev;
}

/* Function to push a node */
void push(struct Node** head_ref, int new_data)
{
    struct Node* new_node
        = (struct Node*)malloc(sizeof(struct Node));
    new_node->data = new_data;
    new_node->next = (*head_ref);
    (*head_ref) = new_node;
}

/* Function to print linked list */
void printList(struct Node* head)
{
    struct Node* temp = head;
    while (temp != NULL) {
        printf("%d ", temp->data);
        temp = temp->next;
    }
}

/* Driver code*/
int main()
{
    /* Start with the empty list */
    struct Node* head = NULL;

    push(&head, 10);
    push(&head, 14);
    push(&head, 19);
    push(&head, 25);

    printf("Given linked list\n");
    printList(head);
    reverse(&head);
    printf("\nReversed linked list \n");
    printList(head);
    getchar();
}

Output

Given linked list
25 19 14 10 
Reversed linked list 
10 14 19 25 

Conclusion

In this C coding interview questions and answers, we’ve compiled a wide-range of practice questions suitable for individuals at all levels, from beginners to advanced learners. Exploring these questions and their solutions will not only enhance your proficiency in C but also prepare you for a successful coding interview experience.

C Coding Interview Questions – FAQs

Q: What are the most common C coding interview questions?

The most common C coding interview questions are designed to test your knowledge of the following topics:

• C syntax and semantics
• Data structures and algorithms
• Memory management
• Pointers
• File I/O

Some specific examples of common C coding interview questions include:

• Reverse a linked list.
• Implement a binary search tree.
• Write a function to find the maximum element in an array.
• Explain the difference between a pointer and an array.
• What is the difference between a function declaration and a function definition?
• How do you allocate memory on the heap?
• How do you free memory that has been allocated on the heap?
• What is a dangling pointer?
• How do you read and write data to a file?

Q. Who can benefit from these C coding interview questions and answers?

These questions are designed to benefit anyone preparing for a C coding interview. Whether you’re a beginner looking to learn the fundamentals or an experienced programmer aiming to enhance your C skills, this resource can assist you in your preparation.

Q: How can I use these questions effectively in my interview preparation?

Start by assessing your current level of expertise in C programming language. Then, you can use these questions to gradually build your skills up and knowledge. Practice solving them on your own, and review the explanations to ensure a thorough understanding.