Implementing a simple queue in C

Question

I am learning C and I have some trouble with pointers. I decided to create a queue to practice a bit. The program works as intended, however I want to know some good practices and suggestions.

Here is queue.c:

#include <stdlib.h>
#include "bank_sim.h" 
#include "queue.h"

void initiliaze(Queue *queue) {
        queue->head = NULL;
        queue->tail = NULL;
}

void enqueue(Queue *queue, Customer *customer) {
        if (queue->head == NULL) {
                queue->head = customer;
                queue->tail = customer;
                queue->customer_cnt++;
        } else {
                queue->tail->next = customer;
                queue->tail = customer;
                queue->customer_cnt++;
        }
}

Customer *dequeue(Queue *queue) {
        if (queue->head == NULL) {
                return NULL;
        } else {
                Customer *head_customer = queue->head;
                queue->head = queue->head->next;
                head_customer->next = NULL;
                queue->customer_cnt--;
                return head_customer;
        }
}

queue.h:

#ifndef QUEUE_H
#define QUEUE_H
#include "bank_sim.h"

typedef struct {
        Customer *head;
        Customer *tail;
        int customer_cnt;
} Queue;

void initiliaze(Queue *queue);
void enqueue(Queue *queue, Customer *customer);
Customer *dequeue(Queue *queue);

# endif

Finally bank_sim.h:

#ifndef BANK_SIM_H
#define BANK_SIM_H

typedef struct Customer Customer;

struct Customer {
        int id;
        int service_time;
        struct Customer *next;
};

typedef struct {
        Customer *customer;
        int occupied;
} Bank_Teller;

#endif

Comments regarding anything is welcome including whether my structure for Customer and Queue can be improved.

Answer 1

One major thing: Queue consists of node which consist of data. Here, your data is Customer. Data should not be coupled with the Queue i.e. think this way.

   typedef struct Node{
         Node* next; // navigation pointer.
         Customer customer; // data
   }Node;

Considering the current implementation, here are a few points to go with:

1. Initialize misses to initialize customer_cnt = 0;.

2. Where are you allocating the Queue instance. Instead, have getQueueNode which allocates memory for the node and initialise that as well. Allocation at one place helps for e.g: easy debugging when malloc returns null due to insufficient memory.

3. Extract common code outside the if-else block in enqueue().

4. Put related code at once i.e. in dequeue operations for head_customer could be consecutive.