Linked Queue in Data Structure

Linked Queue in Data Structure example in C programming :

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

struct qnode {
  int data;
  int prio;
  struct qnode *next;
};

void quein(struct qnode **, struct qnode **, int, int);
int quedel(struct qnode **, struct qnode **, int *, int *);

int main(void) {
  int tab[10] = { 2, 8, 3, 5, 4, 9, 6, 7, 1, 0 };
  struct qnode *first = NULL;
  struct qnode *last = NULL;
  int val, prio, i;

  for (i = 0; i < 10; i++) {
    val = tab[i], prio = i;
    printf("Inserting: value: %d with priority: %d\n", prio, val);
    quein(&first, &last, val, prio);
  }

  printf("=-=\n");

  for (i = 0; i < 11; i++) {
    val = tab[i], prio = i;
    if (quedel(&first, &last, &val, &prio) != -1)
      printf("Deleting: value: %d with priority: %d\n", prio, val);
  }

  return 0;
}

int quedel(struct qnode **first, struct qnode **last, int *prio, int *val) {
  struct qnode *tmp = NULL;

  if ((NULL == *last) && (*last == *first)) {
    fprintf(stderr, "Empty queue.....\n");
    return -1;
  }

  *val = (*first)->data, *prio = (*first)->prio;
  tmp = *first, *first = (*first)->next;

  if (*last == tmp)
    *last = (*last)->next;
  free(tmp);

  return 0;
}

void quein(struct qnode **first, struct qnode **last, int prio, int val) {
  struct qnode *tmp = NULL;
  struct qnode *tmp1 = NULL;

  tmp = malloc(sizeof(struct qnode));

  tmp->data = val;
  tmp->prio = prio;
  tmp->next = NULL;

  if (*last == NULL) {
    *last = tmp;
    *first = *last;
  } else {
    if ((*first)->prio < prio) {
      tmp->next = *first;
      *first = tmp;
    } else {
      if ((*last)->prio > prio) {
        (*last)->next = tmp;
        *last = tmp;
      } else {
        tmp1 = *first;
        while ((tmp1->next)->prio >= prio) {
          tmp1 = tmp1->next;
        }
        tmp->next = tmp1->next;
        tmp1->next = tmp;
      }
    }

  }

  return;
}

OUTPUT

Empty queue.....
Inserting: value: 0 with priority: 2
Inserting: value: 1 with priority: 8
Inserting: value: 2 with priority: 3
Inserting: value: 3 with priority: 5
Inserting: value: 4 with priority: 4
Inserting: value: 5 with priority: 9
Inserting: value: 6 with priority: 6
Inserting: value: 7 with priority: 7
Inserting: value: 8 with priority: 1
Inserting: value: 9 with priority: 0
=-=
Deleting: value: 5 with priority: 9
Deleting: value: 1 with priority: 8
Deleting: value: 7 with priority: 7
Deleting: value: 6 with priority: 6
Deleting: value: 3 with priority: 5
Deleting: value: 4 with priority: 4
Deleting: value: 2 with priority: 3
Deleting: value: 0 with priority: 2
Deleting: value: 8 with priority: 1
Deleting: value: 9 with priority: 0