What am I doing wrong in my pop function (queue) C - c

Question

I have to write a program that implements a queue with all sorts of menu options (which are all done). I'm having trouble with my "pop" function.
My program is a restaurant waiting list for employees. Whenever a customer calls in or comes into the restaurant they are put onto the waiting list. The only way to pop (be seated) is if the customer's status is waiting-in-restaurant. I have correctly written the portion that changes a customer from call-in to waiting in restaurant.
Also, if the group size is bigger than the table size, I'm supposed to go to the next node and check if the next group fits the criteria to be seated.
enum status(WAIT,CALL);
typedef struct restaurant
{
//stuff
}list;
//I call pop in the main as follows:
pop(&head, &tail);
void pop(list** head, list** tail)
{
list* temp = *head;
int tableSize;
if(*head == *tail && *tail == NULL)
{
printf("The queue is empty... exitting program... \n");
exit(EXIT_FAILURE);
}
printf("What is the table size? ");
scanf(" %d", &tableSize);
if(temp->groupSize > tableSize || temp->waitStatus == CALL)
while(temp->groupSize > tableSize || temp->waitStatus == CALL)
temp = temp->nextNode;
else
*head = (*head)->nextNode;
if(*tail == temp)
*tail = (*tail)->nextNode;
free(temp);
}
When I display my output it doesn't delete the node in the instance if it has to skip the first person in the queue. However, it does work when the first person meets the criteria. Why is this?

Answer 1

First, your pop seems to allow items in the middle of the list to be removed. While this is doable, it requires you remember what was pointing to the node popped to ensure it is set to the node that is after the node being popped. There are a number of ways to do this.
Also, your empty() condition is off. head will always be NULL if the list is empty provided you're doing your job right on setting newly added node nextNode members to NULL. The comparison against tail or checking tail for NULL is not needed.
Finally, perhaps you may want to consider returning the data from the pop if there was any, and a boolean condition of true/false as the function return result to indicate whether something was taken off. Otherwise, how is your program to know data was retrieved successfully, and what that data was?
Regardless, just using your current mantra of deleting something that matches:
void pop(list** head, list** tail)
{
list *temp = NULL, *prior = NULL;
int tableSize = 0;
if(*head == NULL)
{
printf("The queue is empty... exitting program... \n");
exit(EXIT_FAILURE);
}
printf("What is the table size? ");
scanf(" %d", &tableSize);
temp = *head;
while (temp && (temp->groupSize > tableSize || temp->waitStatus == CALL))
{
prior = temp;
temp = temp->nextNode;
}
if (temp)
{
// only way prior is set is if temp is NOT
// pointing to the first node, therefore *head
// is not changed.
if (prior)
{
prior->nextNode = temp->nextNode;
// if we made it to the tail ptr, then it needs
// to be moved back to the prior node
if (*tail == temp)
*tail = prior;
}
else
{ // first node was removed. so move head to
// the next node (which may be NULL)
*head = temp->nextNode;
}
// release the node
free(temp);
}
}