queue.c

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

struct _Node {
    int data;
    struct _Node *next;
};

typedef struct _Node Node;

void enqueue(Node **headElement, Node **tailElement, int data);
int  dequeue(Node **headElement, Node **tailElement);
void show_queue(Node *headElement);

int main()
{
    Node *head = NULL;
    Node *tail = NULL;
    enqueue(&head, &tail, 2);
    enqueue(&head, &tail, 5);
    enqueue(&head, &tail, 1);
    dequeue(&head, &tail);
    show_queue(head);    
    return 0;
}

void enqueue(Node **headElement, Node **tailElement, int data)
{
    Node *node = (Node *)malloc(sizeof(Node));
    node->data = data;
    node->next = NULL; // if you do not do it you might get garbage
    if (!*tailElement) {
        *tailElement = node;
        *headElement = node;
    } else {
        (*tailElement)->next = node;
        *tailElement = node;
    }
}

int dequeue(Node **headElement, Node **tailElement)
{
    Node *node = *headElement;
    int data = node->data;
    *headElement = (*headElement)->next;
    free(node);
    if (!(*headElement)) {
        *tailElement = NULL;
    }

    return data;
}

void show_queue(Node *headElement)
{
    Node *tempNode = headElement;
    int i = 1;
    while(tempNode) {
        printf("Node: %i Data Value: %i\n", i++, tempNode->data);
        tempNode = tempNode->next;
    }   
}