QueueImplementationWithList.c

#include <stdio.h>
#include <stdlib.h>
typedef struct Queue
{
    struct Queue *head;
    struct Queue *next;
    int value;
    int size;
}Queue;
/*
 * create empty queue
*/
Queue *create_queue()
{
    Queue *ret = (Queue*) malloc(sizeof(Queue));
    ret->head = ret->next = NULL;
    ret->size = 0;
    return ret;
}
void enqueue(Queue *q, int value)
{
    Queue *cur = q;
    // queue is empty, initialize head
    if( !q->head )
    {
        Queue *head = (Queue*) malloc(sizeof(Queue));

        if( !head )
        {
            perror("create queue");
            exit(-1);
        }
        head->value = value;
        head->next = NULL;
        cur->head = head;
        cur->size++;
    }
    else
    {
        // go until end of queue
        cur = cur->head;
        while( cur->next )
        {
            cur = cur->next;
        }
        // reached end of queue
        Queue *temp = (Queue*) malloc(sizeof(Queue));
        temp->value = value;
        temp->next = NULL;
        // make last node to point to temp - add the link
        cur->next = temp;
        q->size++;      // increase size
    }
    return;
}
int dequeue(Queue *q)
{
    Queue *cur = q->head;
    int ret = cur->value;
    q->size--;
    // advance the head of the queue
    q->head = q->head->next;
    // free memory
    free(cur);
    cur = NULL;
    return ret;
}
void print_queue(Queue *q)
{
    Queue *cur = q->head;
    printf("[");
    while( cur )
    {
        printf(" %d ", cur->value);
        cur = cur->next;
    }
    printf("]\n");
    return;
}
int main()
{
    Queue *q1 = create_queue();
    enqueue(q1, 5);
    enqueue(q1, 9);
    print_queue(q1);
    int d = dequeue(q1);
    printf("d is %d\n", d);
    print_queue(q1);
    enqueue(q1, 45);
    print_queue(q1);
    return 0;
}