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

#define EMPTY -1

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

struct queue {
    struct node* front;
    struct node* back;
};

void init(struct queue* qPtr);
int enqueue(struct queue* qPtr, int val);
int dequeue(struct queue* qPtr);
int empty(struct queue* qPtr);
int front(struct queue* qPtr);


int main(void) {

    struct queue* MyQuePtr = (struct queue *)malloc(sizeof(struct queue));
    init(MyQuePtr);

    enqueue(MyQuePtr, 3);
    enqueue(MyQuePtr, 5);
    enqueue(MyQuePtr, 7);

    printf("\n dequeue %d ", dequeue(MyQuePtr));
    printf("\n front of the queue %d", front(MyQuePtr));
    printf("\n dequeue %d ", dequeue(MyQuePtr));
    printf("\n dequeue %d ", dequeue(MyQuePtr));

    printf("\n is empty %d ", empty(MyQuePtr));

    return 0;
}

void init(struct queue* qPtr) {
    qPtr->front = NULL;
    qPtr->back = NULL;
}

int enqueue(struct queue* qPtr, int val) {
    struct node* temp;
    temp = (struct node*)malloc(sizeof(struct node));
    if(temp != NULL) {
        temp->data = val;
        temp->next = NULL;

        if(qPtr->back != NULL)
            qPtr->back->next = temp;

        qPtr->back = temp;

        if(qPtr->front == NULL)
            qPtr->front = temp;

        return 1;
    }
    else
        return 0;

    }

int dequeue(struct queue* qPtr) {
    struct node * temp;
    int retval;
    if(qPtr->front == NULL)
        return EMPTY;
    retval = qPtr->front->data;
    temp = qPtr->front;
    qPtr->front = qPtr->front->next;

    if(qPtr->front == NULL)
        qPtr->back = NULL;

    free(temp);

    return retval;
}

int empty(struct queue* qPtr) {
    return qPtr->front == NULL;
}

int front(struct queue* qPtr) {
    if(qPtr->front != NULL)
        return qPtr->front->data;
    else
        return EMPTY;
}