linked_list_queue.c

/*Program of queue using linked list*/
#include<stdio.h>
#include<stdlib.h>
struct node
{
	int info;
	struct node *link;
} *front = NULL, *rear = NULL;
void insert(int item);
int del();
int peek();
int isEmpty();
void display();

int main()
{
	int choice,item;
	while(1)
	{
		printf("1.Insert\n");
		printf("2.Delete\n");
		printf("3.Display the element at the front\n");
		printf("4.Display all elements of the queue\n");
		printf("5.Quit\n");
		printf("Enter your choice: ");
		scanf("%d",&choice);
		switch(choice)
		{
			case 1:
			printf("Input the element for adding in queue: ");
			scanf("%d",&item);
			insert(item);
			break;
			
			case 2:
			printf("Deleted element is %d\n",del());
			break;
			
			case 3:
			printf("Element at the front of queue is %d\n",peek());
			break;
			
			case 4:
			display();
			break;
			
			case 5:
			exit(1);
			
			default:
			printf("Wrong choice\n");
		}/*End of switch()*/
	}/*End of while*/
}/*End of main()*/

void insert(int item)
{
	struct node *tmp;
	tmp = (struct node *)malloc(sizeof(struct node));
	if(tmp == NULL)
	{
		printf("Memory not avaliable\n");
		return;
	}
	tmp->info = item;
	tmp->link = NULL;
	if(front==NULL) /*If queue is empty()*/
		front = tmp;
	else
		rear->link = tmp;
	rear = tmp;
}/*End of insert()*/

int del()
{
	struct node *tmp;
	int item;
	if(isEmpty())
	{
		printf("Queue Underflown\n");
		exit(1);
	}
	tmp = front;
	item = tmp->info;
	front = front->link;
	free(tmp);
	return item;
}/*End of del()*/

int peek()
{
	if(isEmpty())
	{
		printf("Queue Underflow\n");
		exit(1);
	}
	return front->info;
}/*End of peek()*/

int isEmpty()
{
	if(front==NULL)
		return 1;
	else
		return 0;
}/*End of isEmpty()*/

void display()
{
	struct node *ptr;
	ptr = front;
	if (isEmpty())
	{
		printf("Queue is empty\n");
		return;
	}
	printf("Queue elements: \n\n");
	while(ptr!=NULL)
	{
		printf("%d ",ptr->info);
		ptr = ptr->link;
	}
	printf("\n\n");
}/*End of display()*/