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

typedef struct node {
    int element;
    struct node* next;
} Node;

typedef struct queue {
    Node* head;
    Node* tail;
} *Queue;

Queue qCreate() {
    Queue q = malloc(sizeof(struct queue));
    q->head = NULL;
    q->tail = NULL;
    return q;
}

int qEmpty(Queue q) {
    return q->head == NULL;
}

void qPush(Queue q, int element) {
    Node * n = malloc(sizeof(Node));
    n->element = element;
    n->next = NULL;
    if(qEmpty(q)) {
        q->head = q->tail = n;
    } else {
        q->tail->next = n;
        q->tail = n;
    }
}

int qPop(Queue q) {
    assert(!qEmpty(q));
    Node* n = q->head;
    q->head = n->next;
    if(q->head == NULL) {
        q->tail == NULL;
    }
    int element = n->element;
    free(n);
    return element;
}

void qClear(Queue q) {
    Node* iter = q->head;
    Node* tmp;
    while(iter != NULL) {
        tmp = iter;
        iter = iter->next;
        free(tmp);
    }
    q->head = NULL;
    q->tail = NULL;
}

void qFree(Queue q) {
    qClear(q);
    free(q);
}

int main( int argc, char *argv[] ) {
    Queue q = qCreate();
    for(int i = 0; i < 10; i++) {
        qPush(q,i*i);
    }

    while(!qEmpty(q)) printf("%d ", qPop(q));
    printf("\n");

	for(int i = 0; i < 10; i++) qPush(q,i);
    for(int i = 0; i < 5; i++) qPop(q);
    printf("%d\n", qPop(q));
    qClear(q);
    assert(qEmpty(q));
    qFree(q);

	return 0;
}