Advanced Database Management System - Tutorials and Notes: C program to implement queue ADT using singly linked list

Friday, 19 January 2018

C program to implement queue ADT using singly linked list

C program for implementing Queue ADT using singly linked list explained, How to implement Queue ADT using singly linked list? How to implement Queue data structure using linear linked list in C?

C Program for implementation of Queue ADT using linked list


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

struct QueueNode //Node definition
{
int data; //To store the data element
struct QueueNode *next; //To store the pointer to the next node
};
typedef struct QueueNode node;
/* Next two statements declare front and rear pointers to point the first and the last elements respectively. They are set to NULL initially. */
node *front = NULL;
node *rear = NULL; //rear

node* createNode() //Function createNode to create a new node
{
node *temp;
temp = (node *) malloc(sizeof(node)) ; //Dynamic memory allocation
printf("\n Enter data to enqueue : ");
scanf("%d", &temp -> data); //Reads the data for new element enqueued
temp -> next = NULL; //sets the next of new node with NULL
return temp;
}
void enQueue() //To insert an element into the queue
{
node *newnode;
newnode= createNode(); //Calls the createNode function
if(front == NULL) //if front is NULL, the queue is empty
{
/* For the first time insertion, we initialize the front and rear pointers to point to the newly created node by assigning the address of first element of newnode to front and rear in the following two statements */
front = newnode;
rear = newnode;
}
else
{
/* If the queue has nodes in it, the current rear node’s next pointer, ie rear->next is assigned with the address stored in new node. And, the new node becomes the new rear. */
rear -> next = newnode; //here newnode has the starting address of first element in newnode
rear=newnode;
}
printf("\n\n Data added to the Queue..");
}
void deQueue()
{
node *temp;
if(front == NULL)
{
printf("\n\n\t Empty Queue..");
return;
}
/* To dequeue a node, the front pointer has to be set to point to the next node in the queue. (In array implementation, we have incremented front with front + 1). This can be done by assigning the current front node’s next element, ie., front->next to new front. */
temp = front; //current front is stored in a temporary variable
front = front -> next; //what front points to is stored in front
printf("\n\n\t Deleted element from queue is %d ", temp -> data);
free(temp); //free (de-allocate) the memory used for temp
}
void displayQ()
{
node *temp;
if(front == NULL)
{
printf("\n\n\t\t Empty Queue ");
}
else
{
/* From front node, displays the data, ie temp->data and move the pointer to the next node and so on */
temp = front;
printf("\n\n\n\t\t Elements in the Queue are: ");
while(temp != NULL)
{
printf("%5d ", temp -> data); //displays the data in current node
temp = temp -> next; //Assign the current node with the address store in the next pointer
}
}
}

int main()
{
int n;
while(1)
{
printf("\n\n Linked list implementation of Queue operations ");
printf("\n ----------------------------------------------\n");
printf("\n 1. Enqueue ");
printf("\n 2. Dequeue ");
printf("\n 3. Display");
printf("\n 4. Quit ");
printf("\n Enter your choice: ");
scanf("%d", &n);
switch(n)
{
case 1 :
enQueue();
break;
case 2 :
deQueue();
break;
case 3 :
displayQ();
break;
case 4:
return;
}
}
}




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