DynamicQueue

/*
Dynamic Queue : Linked List Representation of Queue
*/
#include <stdio.h>
#include <stdlib.h>
struct node
{
    int data;
    struct node *next;
};

struct node *front = NULL;
struct node *rear = NULL;

// function which inserts node in queue
void enQueue(int value)
{
    struct node *newNode;
 
    // create new node and accept data and set next part as NULL by default
    newNode = (struct node*)malloc(sizeof(struct node)); 
    newNode->next = NULL;
    newNode->data = value;
    
    if ( rear == NULL )         // if rear is NULL, means queue is empty
    {   
        front = newNode;        // as queue is empty, move front as well as rear to newNode
        rear = newNode;         // as queue is empty, move front as well as rear to newNode
    }
    else
    {
        rear->next = newNode;  // place new node next to rear 
        rear = newNode;        // move rear to new inserted node
    }
}

// function which inserts node in queue
void deQueue()
{
    struct node *nodeToDelete;

    if ( front == NULL )         // if ront is NULL, means Queue is empty
    {   
        printf("Queue is empty");
    }
    else
    {
        nodeToDelete = front;
        printf("Deleted Element = %d",nodeToDelete->data);   //display deleted element
        
        if ( front == rear )    // If front == rear, means there is only one node
        {
            front = NULL;
            rear = NULL;
        }
        else
        {
            //front != rear, means there is more than one node, just move front to next node
            front = front->next;
        }
        free(nodeToDelete);
    }
}

// function which displays whole Queue
void displayQueue()
{
    struct node *curr;
    if ( front == NULL )           // if front is NULL, means Queue is empty
    {
        printf("Queue is empty.");  // give error message
    }
    else
    {
        printf("Queue is : |");
        curr = front;                    // Move curr to front of Queue
        while ( curr != NULL )           // move till curr does not become NULL
        {
            printf(" %d |",curr->data);  // display node's data
            curr = curr->next;            // Move curr to next node
        }  
    }
}

int main()
{
    enQueue(10);
    enQueue(20);
    enQueue(30);
    displayQueue();
    deQueue();
    displayQueue();
    return 0;
}