Implemented a queue in C.

queue.c

//
//  main.c
//  Queue
//
//  Created by Julius Schmidt on 24.02.18.
//  Copyright © 2018 Julius Schmidt. All rights reserved.
//

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

typedef struct node {
    struct node* nextNode;
    void* content;
} node;


typedef struct queue {
    node* head;
    node* tail;
    size_t size;
} queue;

void enqueue(queue*, void*);
bool empty(queue*);
void dequeue(queue*);




int main(int argc, const char * argv[]) {
    queue q;
    int exampleElement = 5;
    int exampleElement2 = 56;
    int exampleElement3 = 100;
    enqueue(&q, &exampleElement);
    enqueue(&q, &exampleElement2);
    enqueue(&q, &exampleElement3);
    dequeue(&q);
    
    printf("Size of queue (count elements): %zu\n", q.size);
    printf("First element in queue (cast as integer): %d\n", *((int*)q.head->content));
    printf("Second element in queue (cast as integer): %d\n", *((int*)q.head->nextNode->content));
}

void enqueue(queue* queue, void* element) {
    node* newnode = calloc(1, sizeof(node));
    newnode->content = element;
    
    if (empty(queue)) {
        queue->head = newnode;
        queue->tail = newnode;
        queue->size = 1;
    } else {
        queue->tail->nextNode = newnode;
        queue->tail = newnode;
        queue->size++;
    }
}

void dequeue(queue* queue) {
    if (!empty(queue)) {
        node* oldHead = queue->head;
        queue->head = queue->head->nextNode;
        free(oldHead);
        oldHead = NULL;
    }
}

bool empty(queue* queue) {
    return queue->head == NULL;
}