queue.c

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

queue* queate(int capacity){
    queue* q = malloc(sizeof(queue));
    if (q) {
        q->first = 0;
        q->size = 0;
        q->capacity = capacity;
        q->data = malloc(capacity * sizeof(int));
    }
    return q;
}

int enqueue(queue* q, int key){
    if (!q) return 0;

    if (q->size == q->capacity)
        return 0;

    int position = (q->first + q->size) % q->capacity;
    q->data[position] = key;  

    q->size++;
    return 1;
}

int* dequeue(queue* q){
    if (q == NULL) return q;
    else if (q->size > 0) {
        int ex = q->first;

        q->first = (q->first + 1) % q->capacity;
        q->size--;

        int* d = q->data[ex];
        return d;
    } 
    else return NULL;
}

void free_queue(queue* q){
    if (q) {
        // if q->data stores pointers of any kind, they should be freed too
        free(q->data);
    } free(q);
}

void printq(queue* q){
    if (q != NULL) {
        
        if (q->size > 0) {
            int pos = q->first;
            for (int i = 0; i < q->size - 1; i++) {
                printf("%d ", q->data[pos]);
                pos = (pos + 1) % q->capacity;
            } printf("%d\n", q->data[pos]);
        } else 
            printf("The queue is empty.\n");
    } 

    else printf("There is no queue.\n");
}