C Language Coding Questions and Answers

Write a C program to swap two numbers without using a temporary variable.

Use the following code to swap two numbers:

Use the following code:

                   
 #include <stdio.h>
 int main() {
 int a = 5, b = 10;
 a = a + b;
 b = a - b;
 a = a - b;
 printf("After swapping: a = %d, b = %d", a, b);
 return 0;

Write a C program to find the factorial of a number using recursion.

Use the following code:

 #include <stdio.h>
 int factorial(int n) {
 if (n == 0) return 1;
 else return n * factorial(n - 1);
 }
 int main() {
   int num = 5;
   printf("Factorial of %d is %d", num, factorial(num));
   return 0;
 }

Write a C program to reverse a string.

Use the following code:

 #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", str);
       return 0;
    }

Write a C program to check if a number is prime.

Use the following code:

 #include <stdio.h>
 int isPrime(int n) {
 if (n <= 1) return 0;
 for (int i = 2; i <= n / 2; i++) {
    if (n % i == 0) return 0;
   }
     return 1;
    }
    int main() {
        int num = 29;
        if (isPrime(num))
            printf("%d is a prime number", num);
        else
            printf("%d is not a prime number", num);
        return 0;
    }

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

Use the following code:

 #include <stdio.h>
 int gcd(int a, int b) {
 if (b == 0)
    return a;
    return gcd(b, a % b);
   }
    int main() {
        int a = 56, b = 98;
        printf("GCD of %d and %d is %d", a, b, gcd(a, b));
        return 0;
    }

Write a C program to implement binary search.

Use the following code:

#include <stdio.h>
int binarySearch(int arr[], int n, int x) {
    int left = 0, right = n - 1;
    while (left <= right) {
        int mid = left + (right - left) / 2;
        if (arr[mid] == x) return mid;
        if (arr[mid] < x) left = mid + 1;
        else right = mid - 1;
    }
    return -1;
}
int main() {
    int arr[] = {2, 3, 4, 10, 40};
    int n = sizeof(arr) / sizeof(arr[0]);
    int x = 10;
    int result = binarySearch(arr, n, x);
    if (result != -1)
        printf("Element is present at index %d", result);
    else
        printf("Element is not present in array");
    return 0;
}

Write a C program to implement bubble sort.

Use the following code:

#include <stdio.h>
void bubbleSort(int arr[], int n) {
    for (int i = 0; i < n-1; i++) {
        for (int j = 0; j < n-i-1; j++) {
            if (arr[j] > 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]);
    bubbleSort(arr, n);
    printf("Sorted array: ");
    for (int i=0; i < n; i++)
        printf("%d ", arr[i]);
    return 0;
}

Write a C program to implement selection sort.

Use the following code:

#include <stdio.h>
void selectionSort(int arr[], int n) {
    for (int i = 0; i < n-1; i++) {
        int min_idx = i;
        for (int j = i+1; j < n; j++)
            if (arr[j] < arr[min_idx])
                min_idx = j;
        int temp = arr[min_idx];
        arr[min_idx] = arr[i];
        arr[i] = temp;
    }
}
int main() {
    int arr[] = {64, 25, 12, 22, 11};
    int n = sizeof(arr)/sizeof(arr[0]);
    selectionSort(arr, n);
    printf("Sorted array: ");
    for (int i=0; i < n; i++)
        printf("%d ", arr[i]);
    return 0;
}

Write a C program to implement insertion sort.

Use the following code:

#include <stdio.h>
void insertionSort(int arr[], int n) {
    for (int i = 1; i < n; i++) {
        int key = arr[i];
        int j = i - 1;
        while (j >= 0 && arr[j] > key) {
            arr[j + 1] = arr[j];
            j = j - 1;
        }
        arr[j + 1] = key;
    }
}
int main() {
    int arr[] = {12, 11, 13, 5, 6};
    int n = sizeof(arr)/sizeof(arr[0]);
    insertionSort(arr, n);
    printf("Sorted array: ");
    for (int i=0; i < n; i++)
        printf("%d ", arr[i]);
    return 0;
}

Write a C program to find the length of a string without using a built-in function.

Use the following code:

#include <stdio.h>
int stringLength(char *str) {
    int length = 0;
    while (*str != '\0') {
        length++;
        str++;
    }
    return length;
}
int main() {
    char str[] = "Hello World";
    printf("Length of string: %d", stringLength(str));
    return 0;
}

Write a C program to merge two sorted arrays.

Use the following code:

#include <stdio.h>
void merge(int arr1[], int arr2[], int n1, int n2, int arr3[]) {
    int i = 0, j = 0, k = 0;
    while (i < n1 && j < n2) {
        if (arr1[i] < arr2[j])
            arr3[k++] = arr1[i++];
        else
            arr3[k++] = arr2[j++];
    }
    while (i < n1)
        arr3[k++] = arr1[i++];
    while (j < n2)
        arr3[k++] = arr2[j++];
}
int main() {
    int arr1[] = {1, 3, 5, 7};
    int n1 = sizeof(arr1)/sizeof(arr1[0]);
    int arr2[] = {2, 4, 6, 8};
    int n2 = sizeof(arr2)/sizeof(arr2[0]);
    int arr3[n1+n2];
    merge(arr1, arr2, n1, n2, arr3);
    printf("Merged array: ");
    for (int i=0; i < n1+n2; i++)
        printf("%d ", arr3[i]);
    return 0;
}

Write a C program to find the sum of digits of a number.

Use the following code:

#include <stdio.h>
int sumOfDigits(int n) {
    int sum = 0;
    while (n != 0) {
        sum += n % 10;
        n /= 10;
    }
    return sum;
}
int main() {
    int num = 1234;
    printf("Sum of digits of %d is %d", num, sumOfDigits(num));
    return 0;
}

Write a C program to check if a number is a palindrome.

Use the following code:

#include <stdio.h>
int isPalindrome(int n) {
    int original = n, reversed = 0;
    while (n != 0) {
        int digit = n % 10;
        reversed = reversed * 10 + digit;
        n /= 10;
    }
    return original == reversed;
}
int main() {
    int num = 121;
    if (isPalindrome(num))
        printf("%d is a palindrome", num);
    else
        printf("%d is not a palindrome", num);
    return 0;
}

Write a C program to find the largest of three numbers.

Use the following code:

#include <stdio.h>
int main() {
    int a = 10, b = 20, c = 15;
    if (a >= b && a >= c)
        printf("Largest number is %d", a);
    else if (b >= a && b >= c)
        printf("Largest number is %d", b);
    else
        printf("Largest number is %d", c);
    return 0;
}

Write a C program to find the Fibonacci series up to a given number.

Use the following code:

#include <stdio.h>
void printFibonacci(int n) {
    int t1 = 0, t2 = 1, nextTerm = 0;
    printf("Fibonacci Series: %d, %d", t1, t2);
    nextTerm = t1 + t2;
    while (nextTerm <= n) {
        printf(", %d", nextTerm);
        t1 = t2;
        t2 = nextTerm;
        nextTerm = t1 + t2;
    }
}
int main() {
    int n = 50;
    printFibonacci(n);
    return 0;
}

Write a C program to reverse a linked list.

Use the following C code:

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

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

void push(Node** head_ref, int new_data) {
    Node* new_node = (Node*) malloc(sizeof(Node));
    new_node->data = new_data;
    new_node->next = (*head_ref);
    (*head_ref) = new_node;
}

void printList(Node *node) {
    while (node != NULL) {
        printf("%d - ", node->data);
        node = node->next;
    }
    printf("NULL\n");
}

void reverse(Node** head_ref) {
    Node* prev = NULL;
    Node* current = *head_ref;
    Node* next = NULL;
    while (current != NULL) {
        next = current->next;
        current->next = prev;
        prev = current;
        current = next;
    }
    *head_ref = prev;
}

int main() {
    Node* head = NULL;
    push(&head, 20);
    push(&head, 15);
    push(&head, 10);
    push(&head, 5);

    printf("Original List: ");
    printList(head);

    reverse(&head);

    printf("Reversed List: ");
    printList(head);

    return 0;
}

Write a C program to check if two strings are anagrams.

Use the following C code:

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

#define CHAR_COUNT 256

int areAnagrams(char* str1, char* str2) {
    int count[CHAR_COUNT] = {0};
    int i;

    if (strlen(str1) != strlen(str2)) return 0;

    for (i = 0; str1[i] && str2[i]; i++) {
        count[str1[i]]++;
        count[str2[i]]--;
    }

    for (i = 0; i < CHAR_COUNT; i++) {
        if (count[i]) return 0;
    }
    return 1;
}

int main() {
    char str1[] = "listen";
    char str2[] = "silent";

    if (areAnagrams(str1, str2)) {
        printf("The strings are anagrams.\n");
    } else {
        printf("The strings are not anagrams.\n");
    }

    return 0;
}

Write a C program to find the longest common prefix of an array of strings.

Use the following C code:

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

#define MAX 100

char* longestCommonPrefix(char* strs[], int strsSize) {
    if (strsSize == 0) return "";

    char* prefix = strs[0];
    for (int i = 1; i < strsSize; i++) {
        while (strncmp(prefix, strs[i], strlen(prefix)) != 0) {
            prefix[strlen(prefix) - 1] = '\0';
        }
    }
    return prefix;
}

int main() {
    char* strs[] = {"flower", "flow", "flight"};
    int strsSize = sizeof(strs) / sizeof(strs[0]);

    printf("Longest Common Prefix: %s\n", longestCommonPrefix(strs, strsSize));

    return 0;
}

Write a C program to implement a basic stack using an array.

Use the following C code:

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

#define MAX 100

typedef struct {
    int top;
    int arr[MAX];
} Stack;

void init(Stack* stack) {
    stack->top = -1;
}

int isFull(Stack* stack) {
    return stack->top == MAX - 1;
}

int isEmpty(Stack* stack) {
    return stack->top == -1;
}

void push(Stack* stack, int value) {
    if (isFull(stack)) {
        printf("Stack overflow\n");
        return;
    }
    stack->arr[++stack->top] = value;
}

int pop(Stack* stack) {
    if (isEmpty(stack)) {
        printf("Stack underflow\n");
        return -1;
    }
    return stack->arr[stack->top--];
}

int peek(Stack* stack) {
    if (isEmpty(stack)) {
        printf("Stack is empty\n");
        return -1;
    }
    return stack->arr[stack->top];
}

int main() {
    Stack stack;
    init(&stack);

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

    printf("Top element: %d\n", peek(&stack));
    printf("Popped element: %d\n", pop(&stack));
    printf("Top element after pop: %d\n", peek(&stack));

    return 0;
}

Write a C program to find all unique pairs in an array that sum up to a given number.

Use the following C code:

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

void findPairs(int arr[], int size, int sum) {
    int* hash = (int*) calloc(size, sizeof(int));
    printf("Pairs with sum %d:\n", sum);

    for (int i = 0; i < size; i++) {
        int complement = sum - arr[i];
        if (complement >= 0 && hash[complement] != 0) {
            printf("%d + %d = %d\n", arr[i], complement, sum);
        }
        hash[arr[i]] = 1;
    }
    free(hash);
}

int main() {
    int arr[] = {1, 4, 6, 8, 10};
    int size = sizeof(arr) / sizeof(arr[0]);
    int sum = 10;

    findPairs(arr, size, sum);

    return 0;
}