Priority Circular Queue (Priority Queue inside Circular Queue) Implementation in C

priority_circular_queue.c

#include <stdio.h>
#include <stdlib.h> // For qsort
#define QUEUESIZE 10 // Number of items the Queue can hold
typedef enum { false, true } bool;  // Use #include <stdbool.h> if available

typedef struct {
    char name[10];
    int priority;
} Item;

Item *templist[QUEUESIZE]; // Used for sorting

typedef struct {
    Item *q[QUEUESIZE+1];		// queue container
    int first;                  // index of first element
    int last;                   // index of last element
    int count;                  // number of elements currently in queue
} Queue;


init_queue(Queue *q) {
    q->first = 0;
    q->last = QUEUESIZE-1;
    q->count = 0;
}

int cmpfunc (const void * a, const void * b) {
    // Modify this function to do comparision on structure's other properties
    return ((*(Item**)a)->priority > (*(Item**)b)->priority);
}

void enqueue(Queue *q, Item *x){
    if (q->count >= QUEUESIZE) {
        printf("Queue overflow\n");
    } else {
        q->last = (q->last+1) % QUEUESIZE;
        q->q[ q->last ] = x;    
        q->count = q->count + 1;                
    }
}

Item *dequeue(Queue *q) {
    Item *x;

    if (q->count <= 0) {
        printf("Queue empty\n");
    } else {
        x = q->q[ q->first ];
        q->first = (q->first+1) % QUEUESIZE;
        q->count = q->count - 1;
    }

    return(x);
}

void enqueue_with_priority(Queue *q, Item *x) {
	int i, count;
	enqueue(q, x);
	count = q->count;
	for(i=0; i < count; ++i) {
		templist[i] = dequeue(q);
	}
    qsort(templist, count, sizeof(Item *), cmpfunc);
    for(i=0; i < count; ++i ) {
    	enqueue(q, templist[i]);
    }

}

int empty(Queue *q) {
    return q->count <= 0 ? true : false;
}


int main() {
    Queue item_queue;
    init_queue(&item_queue);

    Item apple = {"apple", 10};
    Item ball = {"ball", 2};
    Item onion = {"onion", 8};

    enqueue_with_priority(&item_queue, &apple);
    enqueue_with_priority(&item_queue, &ball);
    enqueue_with_priority(&item_queue, &onion);

    dequeue(&item_queue);
    dequeue(&item_queue);
    dequeue(&item_queue);

    return empty(&item_queue) ? 0 : -1;
}