Program: Linked Queue

#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;
}

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