DynamicQueueUsingDoublePointer

/**
 Dynamic Queue Using double pointer
*/

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

struct node
{
    int data;
    struct node *next;
};

// function which inserts node in queue
void enQueue(struct node **front,struct node **rear,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 **front,struct node **rear)
{
    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 **front,struct node **rear)
{
    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()
{
    struct node *front = NULL,*rear = NULL;
    enQueue(&front,&rear,10);
    enQueue(&front,&rear,20);
    enQueue(&front,&rear,30);
    displayQueue(&front,&rear);
    deQueue(&front,&rear);
    displayQueue(&front,&rear);
    return 0;
}