C Programming Code Examples

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Implement various Queue Functions using Dynamic Memory Allocation

Implement various Queue Functions using Dynamic Memory Allocation

- Use malloc function to allocate memory.
- Define separate functions for the operations like insert, delete and display.
- Use switch statement to access these functions.

    #include <stdio.h>

    #include <stdlib.h>

    #define MAX 10

    struct node

    {

        int data;

        struct node *link;

    }*front, *rear;

    // function protypes

    void insert();

    void delete();

    void queue_size();

    void check();

    void first_element();

    void main()

    {

        int choice, value;

        while(1)

        {

            printf("enter the choice \n");

            printf("1 : create an empty queue \n2 : Insert element\n");

            printf("3 : Dequeue an element \n4 : Check if empty\n");

            printf("5. Get the first element of the queue\n");

            printf("6. Get the number of entries in the queue\n");

            printf("7. Exit\n");

            scanf("%d", &choice);

            switch (choice)    // menu driven program

            {

            case 1: 

                printf("Empty queue is created with a capacity of %d\n", MAX);

                break;

            case 2:    

                insert();

                break;

            case 3: 

                delete();

                break;

            case 4: 

                check();

                break;

            case 5: 

                first_element();

                break;

            case 6: 

                queue_size();

                break;

            case 7: 

                exit(0);

            default: 

                printf("wrong choice\n");

                break;

            }

        }

    }

    // to insert elements in queue

    void insert()

    {

        struct node *temp;

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

        printf("Enter value to be inserted \n");

        scanf("%d", &temp->data);

        temp->link = NULL;

        if (rear  ==  NULL)

        {

            front = rear = temp;

        }

        else

        {

            rear->link = temp;

            rear = temp;

        }    

    }

    // delete elements from queue

    void delete()

    {

        struct node *temp;

        temp = front;

        if (front == NULL)

        {

            printf("queue is empty \n");

            front = rear = NULL;

        }

        else

        {    

            printf("deleted element is %d\n", front->data);

            front = front->link;

            free(temp);

        }

    }

    // check if queue is empty or not

    void check()

    {

        if (front == NULL)

            printf("\nQueue is empty\n");

        else

            printf("Elements are present in the queue \n");

    }

    // returns first element of queue

    void first_element()

    {

        if (front == NULL)

        {

            printf(" The queue is empty \n");

        }

        else

            printf(" The front element is %d \n", front->data);        

    }

    // returns number of entries and displays the elements in queue

    void queue_size()

    {

        struct node *temp;

        temp = front;

        int cnt = 0;

        if (front  ==  NULL)

        {

            printf(" queue empty \n");

        }

        while (temp)

        {

            printf("%d  ", temp->data);

            temp = temp->link;

            cnt++;

        }

        printf(" size of queue is %d  \n", cnt);

    }

- Ask the user for the operations like insert, delete, display etc.
- According to the entered option access the respective functions. Use switch statement to access the functions.
- Use structure with a data and a pointer as the data module. Use malloc function to assign the memory dynamically.
- In the insert() function ask the user to enter the number to be inserted and store the value into the new data module's data.
- In the delete() function delete the element at the front.
- In the check() function, check if the queue is empty or not.
- In the first_element() function, print the first element of the queue.