Simple implementation of a queue using linked list in C

queue.c

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

typedef struct node {
    int val;
    struct node *next;
} node_t;

void enqueue(node_t **head, int val) {
    node_t *new_node = malloc(sizeof(node_t));
    if (!new_node) return;

    new_node->val = val;
    new_node->next = *head;

    *head = new_node;
}

int dequeue(node_t **head) {
    node_t *current, *prev = NULL;
    int retval = -1;

    if (*head == NULL) return -1;

    current = *head;
    while (current->next != NULL) {
        prev = current;
        current = current->next;
    }

    retval = current->val;
    free(current);
    
    if (prev)
        prev->next = NULL;
    else
        *head = NULL;

    return retval;
}

void print_list(node_t *head) {
    node_t *current = head;

    while (current != NULL) {
        printf("%d\n", current->val);
        current = current->next;
    }
}

int main() {
    node_t *head = NULL;
    int ret;

    enqueue(&head, 11);
    enqueue(&head, 22);
    enqueue(&head, 33);
    enqueue(&head, 44);

    print_list(head);
    
    while ((ret=dequeue(&head)) > 0) {
        printf("dequeued %d\n", ret);
    }
    printf("done. head=%p\n", head);

    return 0;
}

You can change it to hold pointers instead of integers

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

typedef struct elem {
    int Data;
    struct elem *next;
} TElem;

TElem *createElem(int i) {
    TElem *newElem = malloc(sizeof(TElem));
    newElem -> Data = i;
    newElem -> next = NULL;
    return newElem;
}

void addToQ(TElem *newElem, TElem **Head, TElem **Tail) {
    newElem -> next = *Head;
    *Head = newElem;
    if (newElem -> next == NULL) {
        *Tail = newElem;
    }
}

void getQ(TElem *Head) {
    TElem *temp = Head;
    while (temp != NULL) {
        printf("element %d\n", temp -> Data);
        temp = temp -> next;
    }
}

int main() {
    TElem *Head = NULL;
    TElem *Tail = NULL;
    for (int i = 0; i < 10; i++) {
        addToQ(createElem(i), &Head, &Tail);
    }
    getQ(Head);
}