Memory Leaks in pop() for A Queue - c

Question

My pop function does not seem to work as it should. Basically, my queue has a pointer to the first and last elements.
My pop functions starts by freeing the first element and assigning it to NULL.
Then it uses the pointer curr to get to the next element each time until it find a NULL.
Finally, my the first pointer in my queue gets assigned to prev, which was pointing to the last element before my curr reached null.
#include <stdlib.h>
struct Queue {
struct Node* first;
struct Node* last;
};
struct Node {
Item val;
struct Node* next;
};
void initQueue (struct Queue **queue){
(*queue) = malloc(sizeof(struct Queue));
(*queue)->first = NULL;
(*queue)->last = NULL;
}
struct Node* createNewNode(){
struct Node *newNode;
newNode = malloc(sizeof(struct Node));
newNode->next = NULL;
return newNode;
}
void push (Item val, struct Queue *queue){
struct Node* newNode = createNewNode();
newNode->val = val;
if(queue->first == NULL){
queue->first = newNode;
queue->last = newNode;
}
else{
newNode->next = queue->last;
queue->last = newNode;
}
}
void pop(struct Queue *queue){
struct Node* curr = queue->last;
struct Node* prev = queue->last;
free(queue->first);
queue->first = NULL;
while(curr != NULL){
prev = curr;
curr = curr->next;
}
queue->first = prev;
}

Answer 1

To pop from the front of the list, simply have first point to first->next.
void pop(struct Queue *queue)
{
if (NULL != queue->first) {
struct Node *first = queue->first;
// Update first ptr
queue->first = queue->first->next;
free(first);
// Only need to update tail if list is empty
if (NULL == queue->first) {
queue->last = NULL;
}
}
}
EDIT
Based on your comment it looks like you aren't seeing what I'm doing, so here's an example.
Assume the queue looks like this:
queue->first
↓
A → B → C → D ← queue->last
First, make a temporary pointer and have it point to queue->first. Then move queue->first so that it points to queue->first->next. The list now looks like:
queue->first
↓
A → B → C → D ← queue->last
↑
first (temp var)
Then, delete the temp var and the list is:
queue->first
↓
B → C → D ← queue->last
EDIT 2 I also notice your push function is incorrect. In a queue, you add new items to the end of the list and take items from the front (FIFO - First In First Out). Like people lining up to see a show. The first person to get there and get in line will be the first to enter the theater. And the last person to arrive goes to the back of the line. So push should be:
void push (Item val, struct Queue *queue){
struct Node* newNode = createNewNode();
newNode->val = val;
if(queue->first == NULL) {
queue->first = newNode;
queue->last = newNode;
}
else{
queue->last->next = newNode; // Add to END of list
queue->last = newNode;
}
}