Queue Using Singly Linked List

Queue Using Singly Linked List

#include<stdio.h>

#include<stdlib.h>

struct queue

{

            int data;

            struct queue *link;

};

typedef struct queue * NODE;

NODE front = NULL;

NODE rear = NULL;

NODE getnode()

{

            NODE x;

            x = (NODE)malloc(sizeof(struct queue));

            x->link = NULL;

}

void insert_rear(int item)

{

            int val;

            NODE temp, cur;

            temp = getnode();

            temp->data = item;

            /*Case 1: List is empty*/

            if(front == NULL)

            {

                        front = rear =temp;

            }

            else

            {

                        rear->link = temp;

                        rear = rear->link;

            }

}

NODE delete_front()

{

            NODE temp;

            if(front == NULL)

            {

                        printf("\nQueue underflow");

                        return NULL;

            }

            else

            {

                        temp = front;

                        front = front->link;

                        temp->link = NULL;

                        printf("\nItem got deleted is: %d", temp->data);

                        free(temp);

                        return front;

            }

}

void display()

{

            NODE cur;

            if(front == NULL)

            {

                        printf("\nQueue is empty");

             }

            else

            {

                        printf("\nQueue contents are:\n");

                        for(cur = front; cur != rear->link ; cur  = cur->link)

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

            }

}

void main()

{

            int ch, item;

            while(1)

            {

                        printf("\n~~MENU~~");

                        printf("\n1.Insert operation");

                        printf("\n2.Delete operation");

                        printf("\n3.Display");

                        printf("\nEnter your choice: ");

                        scanf("%d",&ch);

                        switch(ch)

                        {

                                    case 1: printf("\nEnter the item to be inserted: ");

                                                scanf("%d", &item);

                                                insert_rear(item);

                                                display();

                                                break;

                                    case 2: front = delete_front();

                                                display();

                                                break;

                                    case 3: display();

                                                break;

                                    case 4: exit(0);

                        }

            }

}

Output

~~MENU~~

1.Insert operation

2.Delete operation

3.Display

Enter your choice: 1

Enter the item to be inserted: 11

Queue contents are:

11

~~MENU~~

1.Insert operation

2.Delete operation

3.Display

Enter your choice: 1

Enter the item to be inserted: 12

Queue contents are:

11        12

~~MENU~~

1.Insert operation

2.Delete operation

3.Display

Enter your choice: 1

Enter the item to be inserted: 13

Queue contents are:

11        12        13

~~MENU~~

1.Insert operation

2.Delete operation

3.Display

Enter your choice: 1

Enter the item to be inserted: 14

Queue contents are:

11        12        13         14

~~MENU~~

1.Insert operation

2.Delete operation

3.Display

Enter your choice: 2

Item got deleted is: 11

Queue contents are:

12        13        14

~~MENU~~

1.Insert operation

2.Delete operation

3.Display

Enter your choice: 2

Item got deleted is: 12

Queue contents are:

13        14

~~MENU~~

1.Insert operation

2.Delete operation

3.Display

Enter your choice: 2

Item got deleted is: 13

Queue contents are:

14

~~MENU~~

1.Insert operation

2.Delete operation

3.Display

Enter your choice: 2

Item got deleted is: 14

Queue is empty

~~MENU~~

1.Insert operation

2.Delete operation

3.Display

Enter your choice: 2

Queue underflow

Queue is empty

~~MENU~~

1.Insert operation

2.Delete operation

3.Display

Enter your choice: 4