Find whether a Number is Prime or Not using Recursion

#include

#include

int primeno(int, int);

int main()

    int num, check;

    clrscr();

    printf("Enter a number: ");

    scanf("%d", &num);

    check = primeno(num, num / 2);

    if (check == 1)

        printf("%d is a prime number\n", num);

    else

        printf("%d is not a prime number\n", num);

    return 0;

int primeno(int num, int i)

    if (i == 1)

        return 1;

    else

       if (num % i == 0)

         return 0;

       else

         return primeno(num, i - 1);

    getch();

Output

Enter a number: 456

456 is not a prime number

Enter a number: 89

89 is a prime number

Find the Factorial of a Number using Recursion

#include

#include

int factorial(int);

int main()

    int num;

    int result;

    clrscr();

    printf("Enter a number to find it's Factorial: ");

    scanf("%d", &num);

    if (num < 0)

        printf("Factorial of negative number not possible\n");

    else

        result = factorial(num);

        printf("The Factorial of %d is %d.\n", num, result);

    return 0;

int factorial(int num)

    if (num == 0 || num == 1)

        return 1;

    else

        return(num * factorial(num - 1));

Output

Enter a number to find it's Factorial: 6

The Factorial of 6 is 720.

#include

#include

int lcm(int, int);

int main()

    int a, b, result;

    int prime[100];

    clrscr();

    printf("Enter two numbers: ");

    scanf("%d%d", &a, &b);

    result = lcm(a, b);

    printf("The LCM of %d and %d is %d\n", a, b, result);

    return 0;

 int lcm(int a, int b)

    static int common = 1;

    if (common % a == 0 && common % b == 0)

        return common;

    common++;

    lcm(a, b);

    return common;

Output

Enter two numbers: 456

The LCM of 456 and 12 is 456

Enter two numbers: 45 75

The LCM of 45 and 75 is 225

#include

#include

int product(int, int);

int main()

    int a, b, result;

    clrscr();

    printf("Enter two numbers to find their product: ");

    scanf("%d%d", &a, &b);

    result = product(a, b);

    printf("Product of %d and %d is %d\n", a, b, result);

    return 0;

int product(int a, int b)

    if (a < b)

        return product(b, a);

    else if (b != 0)

        return (a + product(a, b - 1));

    else

        return 0;

Output

Enter two numbers to find their product: 176 340

Product of 176 and 340 is 59840

#include

#include

#include

void check(char [], int);

int main()

    char word[15];

    clrscr();

    printf("Enter a word to check if it is a palindrome\n");

    scanf("%s", word);

    check(word, 0);

    return 0;

void check(char word[], int index)

    int len = strlen(word) - (index + 1);

    if (word[index] == word[len])

        if (index + 1 == len || index == len)

            printf("The entered word is a palindrome\n");

            return;

        check(word, index + 1);

    else

        printf("The entered word is not a palindrome\n");

Output

Enter a word to check if it is a palindrome

malayalam

The entered word is a palindrome

#include

#include

int gcd(int, int);

int main()

    int a, b, result;

    printf("Enter the two numbers to find their GCD: ");

    scanf("%d%d", &a, &b);

    result = gcd(a, b);

    printf("The GCD of %d and %d is %d.\n", a, b, result);

int gcd(int a, int b)

    while (a != b)

        if (a > b)

            return gcd(a - b, b);

        else

            return gcd(a, b - a);

    return a;

Output

Enter the two numbers to find their GCD: 100 70

The GCD of 100 and 70 is 10.

#include

#include

void binary_search(int [], int, int, int);

void bubble_sort(int [], int);

int main()

    int key, size, i;

    int list[25];

    clrscr();

    printf("Enter size of a list: ");

    scanf("%d", &size);

    printf("Generating random numbers\n");

    for(i = 0; i < size; i++)

        list[i] = rand() % 100;

        printf("%d  ", list[i]);

    bubble_sort(list, size);

    printf("\n\n");

    printf("Enter key to search\n");

    scanf("%d", &key);

    binary_search(list, 0, size, key);

 void bubble_sort(int list[], int size)

    int temp, i, j;

    for (i = 0; i < size; i++)

        for (j = i; j < size; j++)

            if (list[i] > list[j])

                temp = list[i];

                list[i] = list[j];

                list[j] = temp;

void binary_search(int list[], int lo, int hi, int key)

    int mid;

    if (lo > hi)

        printf("Key not found\n");

        return;

    mid = (lo + hi) / 2;

    if (list[mid] == key)

        printf("Key found\n");

    else if (list[mid] > key)

        binary_search(list, lo, mid - 1, key);

    else if (list[mid] < key)

        binary_search(list, mid + 1, hi, key);

Output

Enter size of a list: 10

Generating random numbers

83  86  77  15  93  35  86  92  49  21

Enter key to search

Key found

#include

#include

int binary_conversion(int);

int main()

   int num, bin;

   clrscr();

   printf("Enter a decimal number: ");

   scanf("%d", &num);

   bin = binary_conversion(num);

   printf("The binary equivalent of %d is %d\n", num, bin);

int binary_conversion(int num)

    if (num == 0)

        return 0;

    else

        return (num % 2) + 10 * binary_conversion(num / 2);

Output

Enter a decimal number: 10

The binary equivalent of 10 is 1010

#include

#include

#include

struct node

    int a;

    struct node *next;

};

void generate(struct node **);

void display(struct node *);

void delete(struct node **);

int main()

    struct node *head = NULL;

    generate(&head);

    printf("\nDisplaying the alternate nodes\n");

    display(head);

    delete(&head);

    return 0;

void display(struct node *head)

    static flag = 0;

    if(head != NULL)

        if (!(flag % 2))

           printf("%d  ", head->a);

        flag++;

        display(head->next);

void generate(struct node **head)

    int num, i;

    struct node *temp;

    printf("Enter length of list: ");

    scanf("%d", &num);

    for (i = num; i > 0; i--)

        temp = (struct node *)malloc(sizeof(struct node));

        temp->a = i;

        if (*head == NULL)

            *head = temp;

            (*head)->next = NULL;

        else

            temp->next = *head;

            *head = temp;

void delete(struct node **head)

    struct node *temp;

    while (*head != NULL)

        temp = *head;

        *head = (*head)->next;

        free(temp);

Output

Enter length of list: 10

Displaying the alternate nodes

1  3  5  7  9