C Programming Coding Questions and Answers

Intermediate-level C Programming Coding Questions and Answers challenge you to apply fundamental concepts. At this stage, you are expected to have a strong understanding of variables, loops, functions, arrays, pointers, memory management, and file handling. 

The questions will test your ability to write efficient code, debug common issues, and optimize performance. Learning these topics will prepare you for advanced C programming tasks and real-world software development challenges. Here are some c coding interview questions and answers for Intermediate Level:

1. Difference Between malloc() and calloc().

In basic c interview questions, both malloc() and calloc() are used for dynamic memory allocation, but they differ in how they allocate memory and the number of arguments they take. 

Choosing between malloc() and calloc() depends on whether you need initialized memory. If zero initialization is important, calloc() is the better option. Otherwise, malloc() is sufficient and more efficient for general-purpose allocation.

2. Write a program to reverse a string.

This program demonstrates how to reverse a string in C. The reverse function takes a string as an argument and swaps characters from the beginning and end of the string, moving toward the center. This process continues until the string is entirely reversed.

Here is the code to reverse a string:

#include <stdio.h>
#include <string.h>

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

int main() {
    char str[] = "Hello";
    reverse(str);
    printf("Reversed string: %s\n", str);
    return 0;
}

Output

Reversed string: olleH

Explanation of the code

The reverse function calculates the length of the string using strlen(). A for loop iterates from the start of the string to the middle. In each iteration, characters from the beginning and end are swapped using a temporary variable temp.

After calling reverse in main(), the string "Hello" becomes "olleH", and the reversed string is printed.

3. What is recursion in C? Provide an example.

In this program, we calculate the factorial of a number using recursion. The factorial function calls itself with a reduced value of n until it reaches the base case where n is 0, at which point it returns 1. The recursive calls then accumulate the result to compute the factorial.

#include <stdio.h>

int factorial(int n) {
    if (n == 0) return 1;  // Base case: factorial of 0 is 1
    return n * factorial(n - 1);  // Recursive case
}

int main() {
    int num = 5;
    printf("Factorial: %d\n", factorial(num));
    return 0;
}

Output

Factorial: 120

Explanation of the code

The factorial function is defined recursively. If n is 0, it returns 1 (the base case). Otherwise, it multiplies n by the result of calling factorial(n - 1), progressively reducing n until it reaches 0.

In the main() function, we call factorial(5), which results in 5 * 4 * 3 * 2 * 1 = 120. The output is 120.

4. Check Whether a Number is Prime

In this basic c interview questions, we will check whether a given number is prime. A prime number is a number greater than 1 that has no divisors other than 1 and itself. We will use a function to determine if a number is prime by checking if it is divisible by any number between 2 and its square root.

#include <stdio.h>
#include <stdbool.h>

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

int main() {
    int num;
    printf("Enter a number: ");
    scanf("%d", &num);
    if (isPrime(num))
        printf("%d is a prime number.\n", num);
    else
        printf("%d is not a prime number.\n", num);
    return 0;
}

Output

Enter a number: 11
11 is a prime number.

Explanation of the code

The function isPrime checks if a number n is divisible by any number from 2 to the square root of n. If it is divisible by any of these numbers, it's not prime. The main function takes input and prints whether the number is prime or not.

5. Find the nth Fibonacci Number using Recursion

In this program, we calculate the nth Fibonacci number using recursion. The Fibonacci sequence is a series where each number is the sum of the two preceding ones, starting from 0 and 1. The recursive function calculates the Fibonacci number by calling itself with decreasing values of n.

#include <stdio.h>

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

int main() {
    int n;
    printf("Enter the value of n: ");
    scanf("%d", &n);
    printf("Fibonacci(%d) = %d\n", n, fibonacci(n));
    return 0;
}

Output

Enter the value of n: 6
Fibonacci(6) = 8

Explanation of the code

The program uses a recursive function fibonacci to calculate the nth Fibonacci number. The base case is n <= 1, where it returns n. Otherwise, it calculates the Fibonacci number using the recursive formula fibonacci(n - 1) + fibonacci(n - 2).

6. What is the difference between while, do-while, and for loops?

The while loop checks the condition before execution, making it useful when the number of iterations is not predetermined. The do-while loop executes at least once and then checks the condition, making it useful when an operation must be performed before checking a condition. The for loop is structured with initialization, condition, and increment/decrement, making it suitable when the number of iterations is known beforehand.

7. What is recursion, and how is it different from iteration?

Recursion is a programming technique where a function calls itself to solve a problem. It is useful for problems like factorial calculation, Fibonacci sequence generation, and tree traversals. Iteration, on the other hand, uses loops to repeatedly execute a block of code. Recursion consumes more stack memory, while iteration is generally more efficient in terms of execution speed and memory usage.

8. What is an array, and how is it different from a linked list?

An array is a collection of elements stored in contiguous memory locations, making it easy to access elements using an index. However, arrays have a fixed size and require memory allocation at compile time. A linked list consists of nodes, where each node contains a data value and a pointer to the next node. Linked lists provide dynamic memory allocation, allowing easy insertion and deletion, but accessing elements is slower compared to arrays since traversal is required.

9. What is an inversion in an array and how can you count it in C?

An inversion in an array is a pair (i, j) such that arr[i] > arr[j] and i < j. It helps identify how far an array is from being sorted.

#include <stdio.h> 
int countInversions(int arr[], int n) 
{ int count = 0; 
for (int i = 0; i < n - 1; i++) 
{ 
for (int j = i + 1; j < n; j++) 
{ 
if (arr[i] > arr[j]) count++; 
} 
} return count; 
} 
int main() 
{ int arr[] = {8, 4, 2, 1}; 
int n = sizeof(arr) / sizeof(arr[0]); 
printf("Total Inversions: %d\n", countInversions(arr, n)); 
return 0; 
}

10. How do you perform a circular rotation of an array in C?

Circular rotation is a shift of an array of elements either to the left or right. In array rotation, you may use a swap method to circularly rotate, such as doing an in-place array rotation by flipping the array.

#include <stdio.h>

// Function to perform right circular rotation k times
void rightRotate(int arr[], int n, int k) {
    k = k % n;  // Handle cases where k > n

    for (int i = 0; i < k; i++) {
        int last = arr[n - 1];  // Store the last element

        // Shift elements to the right
        for (int j = n - 1; j > 0; j--)
            arr[j] = arr[j - 1];

        arr[0] = last;  // Place the last element at the first position
    }
}

int main() {
    int arr[] = {1, 2, 3, 4, 5};  // Example array
    int n = 5, k = 2;             // Number of rotations

    rightRotate(arr, n, k);

    printf("Array after circular rotation: ");
    for (int i = 0; i < n; i++)
        printf("%d ", arr[i]);
    printf("\n");

    return 0;
}

11. How can you find the transpose of a rectangular array in C?

The transpose of a matrix flips rows into columns. Useful for operations like matrix multiplication and transformations.

#include <stdio.h>

int main() {
    int rows = 2, cols = 3;  // Original matrix dimensions
    int matrix[2][3] = {
        {1, 2, 3},
        {4, 5, 6}
    };
    int transpose[3][2];  // Transposed matrix dimensions (cols x rows)

    // Compute transpose
    for (int i = 0; i < rows; i++) {
        for (int j = 0; j < cols; j++) {
            transpose[j][i] = matrix[i][j];
        }
    }

    // Print transposed matrix
    printf("Transpose of matrix:\n");
    for (int i = 0; i < cols; i++) {
        for (int j = 0; j < rows; j++) {
            printf("%d ", transpose[i][j]);
        }
        printf("\n");
    }

    return 0;
}

12. How do you perform a spiral traversal of a cuboidal array in C?

Spiral traversal prints matrix elements layer by layer in a clockwise direction. This is commonly used in pattern printing and visualization problems.

#include <stdio.h>

int main() {
    int n = 3;  // Size of the square matrix
    int matrix[3][3] = {
        {1, 2, 3},
        {4, 5, 6},
        {7, 8, 9}
    };

    int top = 0, bottom = n - 1;
    int left = 0, right = n - 1;

    printf("Spiral traversal: ");

    while (top <= bottom && left <= right) {
        // Traverse from left to right along the top row
        for (int i = left; i <= right; i++)
            printf("%d ", matrix[top][i]);
        top++;

        // Traverse from top to bottom along the rightmost column
        for (int i = top; i <= bottom; i++)
            printf("%d ", matrix[i][right]);
        right--;

        // Traverse from right to left along the bottom row
        if (top <= bottom) {
            for (int i = right; i >= left; i--)
                printf("%d ", matrix[bottom][i]);
            bottom--;
        }

        // Traverse from bottom to top along the leftmost column
        if (left <= right) {
            for (int i = bottom; i >= top; i--)
                printf("%d ", matrix[i][left]);
            left++;
        }
    }

    printf("\n");

    return 0;
}

13. How do you find the maximum element in an array using the max-heap concept?

The max-heap property ensures the largest element is at the root. You can mimic this behavior to find the maximum element without implementing a full heap.

#include <stdio.h>

// Function to build a max-heap from an array
void buildMaxHeap(int arr[], int n) {
    for (int i = 0; i < n; i++) {
        int current = i;

        // Heapify up: move current element up until max-heap property is satisfied
        while (current > 0 && arr[(current - 1) / 2] < arr[current]) {
            // Swap current element with its parent
            int temp = arr[current];
            arr[current] = arr[(current - 1) / 2];
            arr[(current - 1) / 2] = temp;

            // Move to parent index
            current = (current - 1) / 2;
        }
    }
}

int main() {
    int arr[] = {10, 30, 20, 50, 40};
    int n = 5;

    buildMaxHeap(arr, n);

    printf("Maximum element using max-heap: %d\n", arr[0]); // Root of max-heap

    return 0;
}

14. How do you reverse the elements of an array in C?

Reversing an array swaps elements from both ends using the swap method.

#include <stdio.h>

// Function to reverse an array
void reverseArray(int arr[], int n) {
    int start = 0, end = n - 1;

    while (start < end) {
        // Swap elements at start and end
        int temp = arr[start];
        arr[start] = arr[end];
        arr[end] = temp;

        start++;
        end--;
    }
}

int main() {
    int arr[] = {5, 10, 15, 20, 25};
    int n = sizeof(arr) / sizeof(arr[0]);  // Calculate array size

    reverseArray(arr, n);  // Reverse the array

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

    return 0;
}

15. Write a program to implement Bubble Sort in C.

Bubble Sort alternates adjacent elements if they are out of order after continuously comparing them.

#include <stdio.h>

// Function to perform Bubble Sort
void bubbleSort(int arr[], int n) {
    for (int i = 0; i < n - 1; i++) {
        // Last i elements are already in place
        for (int j = 0; j < n - i - 1; j++) {
            if (arr[j] > arr[j + 1]) {
                // Swap arr[j] and arr[j+1]
                int temp = arr[j];
                arr[j] = arr[j + 1];
                arr[j + 1] = temp;
            }
        }
    }
}

int main() {
    int arr[] = {64, 34, 25, 12, 22, 11, 90};
    int n = sizeof(arr) / sizeof(arr[0]);  // Calculate array size

    bubbleSort(arr, n);  // Sort the array

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

    return 0;
}

Output:

Sorted array: 11 12 22 25 34 64 90

16. Write a program using Binary Search in C to locate a component within a sorted array.

#include <stdio.h>

// Function to perform binary search on a sorted array
int binarySearch(int arr[], int n, int key) {
    int low = 0, high = n - 1;

    while (low <= high) {
        int mid = (low + high) / 2;

        if (arr[mid] == key) {
            return mid;  // Element found
        } else if (arr[mid] < key) {
            low = mid + 1;  // Search in right half
        } else {
            high = mid - 1; // Search in left half
        }
    }

    return -1;  // Element not found
}

int main() {
    int arr[] = {10, 20, 30, 40, 50};
    int n = sizeof(arr) / sizeof(arr[0]);
    int key = 30;

    int result = binarySearch(arr, n, key);

    if (result != -1)
        printf("Element found at index: %d\n", result);
    else
        printf("Element not found\n");

    return 0;
}

Output:

Element found at index: 2

17. Write a program to implement Merge Sort in C.

#include <stdio.h>

// Function to merge two subarrays of arr[]
void merge(int arr[], int l, int m, int r) {
    int n1 = m - l + 1;
    int n2 = r - m;

    int L[n1], R[n2];

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

    int i = 0, j = 0, k = l;

    // Merge the temporary arrays back into arr[l..r]
    while (i < n1 && j < n2) {
        if (L[i] <= R[j])
            arr[k++] = L[i++];
        else
            arr[k++] = R[j++];
    }

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

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

// Function to perform Merge Sort on arr[l..r]
void mergeSort(int arr[], int l, int r) {
    if (l < r) {
        int m = l + (r - l) / 2; // Find the middle point
        mergeSort(arr, l, m);    // Sort first half
        mergeSort(arr, m + 1, r);// Sort second half
        merge(arr, l, m, r);     // Merge the sorted halves
    }
}

int main() {
    int arr[] = {12, 11, 13, 5, 6, 7};
    int n = sizeof(arr) / sizeof(arr[0]);

    mergeSort(arr, 0, n - 1);

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

    return 0;
}

Output:

Sorted array: 5 6 7 11 12 13

18. Implement Quick Sort in C.

#include <stdio.h>

// Function to partition the array
int partition(int arr[], int low, int high) {
    int pivot = arr[high];  // pivot element
    int i = low - 1;

    for (int j = low; j <= high - 1; j++) {
        if (arr[j] <= pivot) {
            i++;
            // Swap arr[i] and arr[j]
            int temp = arr[i];
            arr[i] = arr[j];
            arr[j] = temp;
        }
    }

    // Swap arr[i+1] and pivot
    int temp = arr[i + 1];
    arr[i + 1] = arr[high];
    arr[high] = temp;

    return i + 1;
}

// Quick Sort function
void quickSort(int arr[], int low, int high) {
    if (low < high) {
        int pi = partition(arr, low, high);  // Partition index
        quickSort(arr, low, pi - 1);         // Sort left subarray
        quickSort(arr, pi + 1, high);        // Sort right subarray
    }
}

int main() {
    int arr[] = {10, 7, 8, 9, 1, 5};
    int n = sizeof(arr) / sizeof(arr[0]);

    quickSort(arr, 0, n - 1);

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

    return 0;
}

Output:

Sorted array: 1 5 7 8 9 10

19. Write a program to implement Heap Sort using heapify in C.

#include <stdio.h>

// Function to maintain max-heap property for subtree rooted at index i
void heapify(int arr[], int n, int i) {
    int largest = i;        // Initialize largest as root
    int left = 2 * i + 1;   // left child
    int right = 2 * i + 2;  // right child

    // If left child is larger than root
    if (left < n && arr[left] > arr[largest])
        largest = left;

    // If right child is larger than current largest
    if (right < n && arr[right] > arr[largest])
        largest = right;

    // If largest is not root, swap and continue heapifying
    if (largest != i) {
        int temp = arr[i];
        arr[i] = arr[largest];
        arr[largest] = temp;

        heapify(arr, n, largest);
    }
}

// Main function to perform heap sort
void heapSort(int arr[], int n) {
    // Build max heap
    for (int i = n / 2 - 1; i >= 0; i--)
        heapify(arr, n, i);

    // Extract elements from heap one by one
    for (int i = n - 1; i >= 0; i--) {
        // Move current root to end
        int temp = arr[0];
        arr[0] = arr[i];
        arr[i] = temp;

        // Call max heapify on the reduced heap
        heapify(arr, i, 0);
    }
}

int main() {
    int arr[] = {12, 11, 13, 5, 6, 7};
    int n = sizeof(arr) / sizeof(arr[0]);

    heapSort(arr, n);

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

    return 0;
}

Output:

Sorted array: 5 6 7 11 12 13

20. Count inversions in an array using Merge Sort in C.

#include <stdio.h>

// Merge two subarrays and count inversions
int mergeAndCount(int arr[], int l, int m, int r) {
    int n1 = m - l + 1;
    int n2 = r - m;

    int L[n1], R[n2];

    for(int i = 0; i < n1; i++) 
        L[i] = arr[l + i];
    for(int j = 0; j < n2; j++) 
        R[j] = arr[m + 1 + j];

    int i = 0, j = 0, k = l, inv_count = 0;

    while(i < n1 && j < n2) {
        if(L[i] <= R[j]) {
            arr[k++] = L[i++];
        } else {
            arr[k++] = R[j++];
            inv_count += (n1 - i); // Count inversions
        }
    }

    while(i < n1) arr[k++] = L[i++];
    while(j < n2) arr[k++] = R[j++];

    return inv_count;
}

// Recursive merge sort that counts inversions
int mergeSortAndCount(int arr[], int l, int r) {
    int inv_count = 0;
    if(l < r) {
        int m = l + (r - l) / 2;
        inv_count += mergeSortAndCount(arr, l, m);
        inv_count += mergeSortAndCount(arr, m + 1, r);
        inv_count += mergeAndCount(arr, l, m, r);
    }
    return inv_count;
}

int main() {
    int arr[] = {1, 20, 6, 4, 5};
    int n = sizeof(arr)/sizeof(arr[0]);

    int inv_count = mergeSortAndCount(arr, 0, n - 1);

    printf("Number of inversions: %d\n", inv_count);
    return 0;
}

Output:

Number of inversions: 5

If you have conquered the intermediate stage, congratulations, you are ready to step into the arena where C truly shines.

C programming coding questions and answers at an advanced level are geared towards those wishing to think like a software architect. This will test your understanding of the language at a deeper level and expose you to problems that are relevant to actual challenges encountered during systems programming and high-performance applications.

You will face questions that will cause you to think critically, debug efficiently, and design solutions that are elegant yet practical. Practicing the following questions will provide you with confidence when answering questions in tough interviews and confidence in solving complex software development issues.

You are now prepared to cater to some of the most interesting coding/engineering interview questions and answers in C, for learners. Below is the next phase of your journey, going from coder to problem-solving pro.

1. Explain file handling in C.

File handling in C is the act of reading from and writing to files using the provided built-in functions. It is often necessary when persistent storage of data is required, as well as reading/writing files of the operating system.

There are many functions provided by the C Standard Library. File handling functions can be split into two groups: functions to open and close a file, and functions to read from or write to a file.

Functions for File Handling in C

2. Write a program to implement binary search using recursion.

In this code, we use a recursive binary search function to find an element in a sorted array. The function binarySearch() takes the sorted array, a low and high index to define the search range, and the key (element to be searched). If the key is found, it returns the index of the key; if not, it returns -1.

#include <stdio.h>

int binarySearch(int arr[], int low, int high, int key) {
    if (low <= high) {
        int mid = (low + high) / 2;
        if (arr[mid] == key) return mid;
        if (arr[mid] > key) return binarySearch(arr, low, mid - 1, key);
        return binarySearch(arr, mid + 1, high, key);
    }
    return -1;
}

int main() {
    int arr[] = {2, 3, 4, 10, 40};
    int n = 5;
    int key = 10;
    int result = binarySearch(arr, 0, n - 1, key);
    printf("Element found at index: %d\n", result);
    return 0;
}

Output:

Element found at index: 3

Explanation of the code:

For the given sorted array { 2, 3, 4, 10, 40 } where the key is 10, the binarySearch() function can be expressed as:

1. The initial interval spans from index 0 to 4 (the whole array). 
2. The middle element is 4, which is located at index 2. Since 4 is smaller than 10, we only search in the array's right half (from index 3 to 4).
3. Now the middle element is at index 3, which is 10. Since this matches the key, the function returns 3 (the index of the key).
4. The main function then prints the index 3.

Thus, the output is "Element found at index: 3".

3. Explain undefined behaviour in C and provide an example.

In C, undefined behavior means the code uses constructs that the C standard does not specify restrictions on. Thus, anything can happen, from crashing the program, to creating a security hole, to having an output that can arise from the system and is entirely nondeterministic.

Example:

#include <stdio.h>

int main() {
    int x;
    printf("%d\n", x); // Using uninitialized variable
    return 0;
}

In this example, x is declared but not initialized before being printed. The output is unpredictable because the value of x is indeterminate.

4. Write a program to implement a stack using linked lists.

A stack is a linear data structure that has a Last In, First Out (LIFO) principle. The element that is added last gets removed first. A linked list is used in this approach to define the stack; each node has a value and a pointer to the node after it.

In this program, I demonstrate simple stack operations: initialization, pushing and popping, and displaying the contents of the stack.

#include <stdio.h>
#include <stdlib.h>

struct Node {
    int data;
    struct Node* next;
};

struct Stack {
    struct Node* top;
};

void initStack(struct Stack* s) {
    s->top = NULL;
}

int isEmpty(struct Stack* s) {
    return s->top == NULL;
}

void push(struct Stack* s, int data) {
    struct Node* newNode = (struct Node*)malloc(sizeof(struct Node));
    newNode->data = data;
    newNode->next = s->top;
    s->top = newNode;
}

int pop(struct Stack* s) {
    if (isEmpty(s)) {
        printf("Stack Underflow\n");
        return -1; // Indicate error
    }
    struct Node* temp = s->top;
    int poppedData = temp->data;
    s->top = s->top->next;
    free(temp);
    return poppedData;
}

void display(struct Stack* s) {
    struct Node* current = s->top;
    while (current != NULL) {
        printf("%d ", current->data);
        current = current->next;
    }
    printf("\n");
}

int main() {
    struct Stack stack;
    initStack(&stack);

    push(&stack, 10);
    push(&stack, 20);
    push(&stack, 30);

    printf("Stack contents: ");
    display(&stack);

    printf("Popped: %d\n", pop(&stack));
    
    printf("Stack contents after pop: ");
    display(&stack);

    return 0;
}

Output:

Stack contents: 30 20 10 
Popped: 30
Stack contents after pop: 20 10

Explanation of the code:

This C program demonstrates a stack data structure implementation using a linked list. A stack follows the Last In, First Out (LIFO) method, which means when things are removed from the list, the last element added to the stack is the first to be removed. The program will push (10,20,30) to the stack in sequential order. The stack after pushing will have the values (30,20,10) top to bottom. The next line will call the pop() function to remove the top item that was in the stack (30) into a variable. The contents of the stack will then be shown again without the 30 being an item in the stack. The stack should now have only 20 and 10 in it.

5. Find out the second largest element in an array

#include <stdio.h>

int main() {
    int arr[] = {12, 34, 10, 6, 40}, largest = arr[0], second = arr[0];
    
    for (int i = 1; i < 5; i++) {
        if (arr[i] > largest) {
            second = largest;
            largest = arr[i];
        } else if (arr[i] > second && arr[i] != largest) {
            second = arr[i];
        }
    }

    printf("Second Largest: %d\n", second);
    return 0;
}

Output:

Second Largest: 34

6. What are pointers in C, and how do they differ from arrays?

A pointer is a variable that accesses or changes another variable directly in memory by containing its address. Pointers give us more options for interactions with memory in the program; for example, pointers are used in dynamic memory allocation, function pointers, or array access/manipulation. 

A collection of variables or fixed size numbers stored consecutively in memory is called an array. An array holds a collection of related indexed variables, while a pointer gives more options related to the allocation and manipulation of memory addresses.

7. Explain the concept of function pointers with an example.

A pointer pointing to a function is called a function pointer. This enables function calls to be dynamic in terms of their values and behaviors. A function pointer allows a function to be passed as an argument to another function, increasing the amount of flexibility for our program. Function pointers are mainly used for callback functions, event handlers, and implementing function tables so the code can execute more efficiently. 

8. What are structures in C, and how do they differ from arrays?

A user-defined data type called a structure unifies linked variables of several data types under a common name. It allows better organization of complex data, such as representing a student with name, age, and marks as attributes. An array, in contrast, is a collection of variables/elements of the same data type stored sequentially in memory. Structures allow for more flexibility because they hold different data types, while arrays will only hold elements of the same data type. 

9. What is a palindrome, and how can we check if a string is a palindrome in C?

 A palindrome is a string that reads the same forward and backwards. We can determine if something is a palindrome by comparing characters from both ends using a character array and reversing the string.

#include <stdio.h>
#include <string.h>
#include <ctype.h>

// Function to check if a string is a palindrome
int isPalindrome(char str[]) {
    int i = 0;
    int j = strlen(str) - 1;

    while (i < j) {
        // Compare characters ignoring case
        if (tolower(str[i]) != tolower(str[j]))
            return 0; // Not a palindrome
        i++;
        j--;
    }
    return 1; // Is a palindrome
}

int main() {
    char str[] = "Level";

    if (isPalindrome(str))
        printf("\"%s\" is a palindrome.\n", str);
    else
        printf("\"%s\" is not a palindrome.\n", str);

    return 0;
}

10. What is an anagram, and how can we check if two strings are anagrams in C?

If two strings, ignoring case sensitivity, contain the same characters at the same frequency, they are anagrams.

#include <stdio.h>
#include <string.h>
#include <ctype.h>

int isAnagram(char str1[], char str2[]) {
    int count[256] = {0};

    // If lengths differ, they can't be anagrams
    if (strlen(str1) != strlen(str2))
        return 0;

    for (int i = 0; str1[i]; i++) {
        count[tolower(str1[i])]++;  // increment for str1
        count[tolower(str2[i])]--;  // decrement for str2
    }

    // If all counts are zero, they are anagrams
    for (int i = 0; i < 256; i++)
        if (count[i] != 0)
            return 0;

    return 1;
}

int main() {
    char str1[] = "Listen";
    char str2[] = "Silent";

    if (isAnagram(str1, str2))
        printf("\"%s\" and \"%s\" are anagrams.\n", str1, str2);
    else
        printf("\"%s\" and \"%s\" are not anagrams.\n", str1, str2);

    return 0;
}

11. How do we count the frequency of characters in a string in C?

To determine how frequently each character occurs in the string, we can utilize a frequency array.

#include <stdio.h>
#include <string.h>

int main() {
    char str[] = "programming";
    int freq[256] = {0};  // Array to store frequency of each ASCII character

    // Count frequency of each character
    for (int i = 0; str[i]; i++)
        freq[(int)str[i]]++;

    // Print frequencies
    printf("Character frequencies:\n");
    for (int i = 0; i < 256; i++)
        if (freq[i] > 0)
            printf("%c : %d\n", i, freq[i]);

    return 0;
}

12. How can we remove spaces and non-alphabetical characters from a string in C?

Loop through the string and copy only alphabetic characters to a new character array.

#include <stdio.h>
#include <ctype.h>

int main() {
    char str[] = "C programming 101!";
    char result[100];  // To store only alphabet characters
    int j = 0;

    // Copy only alphabetic characters
    for (int i = 0; str[i]; i++)
        if (isalpha(str[i]))
            result[j++] = str[i];

    result[j] = '\0';  // Null-terminate the filtered string

    printf("Filtered string: %s\n", result);
    return 0;
}

13. How can we replace a substring in a string in C?

We can find the substring using strstr and replace it by copying parts of the original string into a new character array.

#include <stdio.h>
#include <string.h>

void replaceSubstring(char str[], char old[], char new[]) {
    char buffer[200];  // Temporary buffer to hold the modified string
    char *pos = strstr(str, old);  // Find first occurrence of 'old'

    if (pos) {
        int index = pos - str;    // Index of 'old' in the string
        str[index] = '\0';       // Terminate string at position of 'old'
        strcpy(buffer, str);     // Copy beginning part to buffer
        strcat(buffer, new);     // Append the new substring
        strcat(buffer, pos + strlen(old)); // Append rest of original string after 'old'
        strcpy(str, buffer);     // Copy final result back to original string
    }
}

int main() {
    char str[100] = "Hello World!";
    replaceSubstring(str, "World", "C Programming");
    printf("Updated string: %s\n", str);
    return 0;
}

14. How can we find the first non-repeating character in a string in C?

Use a frequency array to count character occurrences and then find the first character with frequency 1.

#include <stdio.h>
#include <string.h>

int main() {
    char str[] = "programming";
    int freq[256] = {0}; // Array to store frequency of each ASCII character

    // Count frequency of each character
    for (int i = 0; str[i]; i++)
        freq[(int)str[i]]++;

    // Find the first character with frequency 1
    for (int i = 0; str[i]; i++) {
        if (freq[(int)str[i]] == 1) {
            printf("First non-repeating character: %c\n", str[i]);
            break;
        }
    }

    return 0;
}

15. How do you print a pyramid pattern using a for loop in C?

Pyramid patterns are something you see often when it comes to placement interviews. These questions require the management of spaces and stars that form a similar triangle shape that is centered. 

Example: Print a pyramid of height n:

#include <stdio.h>

int main() {
    int n = 5; // Height of the pyramid

    for (int i = 1; i <= n; i++) {
        // Print spaces
        for (int j = 1; j <= n - i; j++)
            printf(" ");
        
        // Print stars
        for (int k = 1; k <= (2 * i - 1); k++)
            printf("*");
        
        printf("\n");
    }

    return 0;
}

Output:

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

16. How do you generate the Fibonacci sequence using a do-while loop in C?

The Fibonacci sequence is a simple sequence of numbers in which each number is the sum of the two numbers before it. A nice way to indicate your understanding of an iterative construct is using a do-while loop. 

Example: Print the first n Fibonacci numbers:

#include <stdio.h> 
int main() 
{ 
int n = 10, a = 0, b = 1, 
count = 0; 
do 
{ 
rintf("%d ", a); 
int next = a + b; a = b; b = next; count++; 
} while (count < n);
printf("\n");
return 0;
}

Output:

0 1 1 2 3 5 8 13 21 34

17. How can you print the n-th row of Pascal's triangle in C?

Pascal's triangle is a pattern of numbers in which the sum of the two numbers above a given number determines that number. The n-th row of a Pascal triangle can be generated using binomial coefficients. 

Example: Print the n-th row of Pascal’s triangle:

#include <stdio.h>

int binomialCoeff(int n, int k) {
    int res = 1;
    for (int i = 0; i < k; ++i) {
        res *= (n - i);
        res /= (i + 1);
    }
    return res;
}

int main() {
    int n = 5;
    for (int k = 0; k <= n; k++)
        printf("%d ", binomialCoeff(n, k));
    printf("\n");
    return 0;
}

Output:

1 5 10 10 5 1

18. How do you print a right-angled triangle pattern using a while loop in C?

Right-angled triangle patterns are another staple of C programming interviews and help demonstrate mastery of loop constructs.

Example:

#include <stdio.h>

int main() {
    int n = 4, i = 1;
    while (i <= n) {
        int j = 1;
        while (j <= i) {
            printf("#");
            j++;
        }
        printf("\n");
        i++;
    }
    return 0;
}

Output:

  # 
 ## 
 ### 
 ####

19. How do you print a number pattern using nested for loops in C?

Number patterns will test your ability to nest loops and manipulate variables. 

Example: Print the following pattern for n = 4:

1 2 3 4 5 6 7 8 9 10

#include <stdio.h>

int main() {
    int n = 4, num = 1;
    for (int i = 1; i <= n; i++) {
        for (int j = 1; j <= i; j++) {
            printf("%d ", num++);
        }
        printf("\n");
    }

Output:

1 
2 3 
4 5 6 
7 8 9 10 

Recap of the Blog:

• Mastered the basics: From variables to loops, functions, arrays, and pointers; you’ll know the building blocks of C as a pro.
• Memory decoded: Distinguish between malloc() and calloc() so that you'll never misuse dynamic memory again.
• Intermediate challenges conquered: Debugging, optimization, and file handling techniques next make the code efficient and strong.
• Advanced concepts unlocked: Memory management, complex data structures, and performance optimizations that most programmers omit, but you won't.
• Interview edge gained: Real coding interview questions and answers that will prepare you to show recruiters.
• Miss this, miss mastery: If you skip over this, you will have gaps in your understanding of the core essentials of C programming. 

In conclusion, learning C language interview questions and answers is essential for anyone pursuing a career in software development. This programming language remains foundational in computer science due to its versatility and efficient use in system-level programming, embedded systems, and application development. 

Whether you're preparing for C language interview questions for freshers or brushing up on advanced concepts for experienced positions, practising these coding challenges and C language interview questions with answers will help build a solid understanding.C programming is not just another programming language; it is the bedrock of every programmer's journey. Can you hone your skills in C Programming Coding Questions and Answers to think logically, write efficient code, and solve complex problems with confidence?

Advice for learners:

• Start with the basics and don’t rush; strong fundamentals make advanced topics easier.
• Practice consistently using coding questions to strengthen problem-solving and debugging skills.
• Explore advanced concepts gradually, like memory management and optimization, to stand out in interviews.

Invest the effort today, and C will pay dividends throughout your software development career.

Here are some frequently asked questions (FAQs) related to C programming coding questions and answers:

1. What are the most common C language interview questions for freshers?

For freshers, the interview questions will tend to be basic in nature, for example, data types, loops or arrays, and functions. For example, you may be asked, "What is a pointer in C?", or "Write a program to find the sum of two numbers," or "What are the basic data types in C?"

2. How do I prepare for C programming coding interviews?

When preparing for a C programming interview, you will want to practice coding problems, understand core concepts such as memory management and pointers, and review common interview questions. 

3. What are some advanced C programming interview questions?

Advanced questions may include recursion, file handling, memory management, and data structures. Examples of these types of questions that may be asked during an interview are, "Explain how malloc() and calloc() differ," or "Write a program to implement a stack using linked lists."

4. What is the importance of understanding pointers in C?

Pointers are extremely important in C programming for several reasons. For one, pointers give you direct manipulation of memory, as well as how to efficiently pass large structures to functions as parameters and perform dynamic memory allocation. It is important to understand memory pointers for low-level operations and for optimizing and improving your code.

5. How do I solve C programming questions for interviews effectively?

Divide the issue into a series of smaller, manageable problems. Write pseudocode, check for edge cases, and then test all of your solutions carefully and thoroughly. Practicing various types of problems will help you improve your skills at problem-solving.

6. What are the key differences between malloc() and calloc()?

malloc() provides memory at runtime with an un-initialized piece of memory, where calloc() provides memory allocated at runtime and initializes all of the bits with all zeros. Understanding these differences helps you remember when to use them and helps you plan your C code's use of memory more efficiently.

7. How can I practice C coding questions for interviews?

In order to get better and improve your C programming skills, leverage different coding standardized application programs like LeetCode, HackerRank, or GeeksforGeeks to practice C programming problems. You could also look for books and resources that are dedicated to C programming interviews so that you can practice C programming problems more methodically.