Queue

Queue - Node

 

#include <stdio.h>
#include <malloc.h>
#define EMPTY 0
 
typedef struct node
{
    int data;
    struct node * link;
} queue;
 
queue * get_node()
{
    queue * tmp;
    tmp = (queue *)malloc(sizeof(queue));
    tmp->link = EMPTY;
    return tmp;
}
 
void enqueue(queue ** front, queue ** rear, int data)
{
    queue * tmp;
    tmp = *rear;
    *rear = get_node();
    (*rear)->data = data;
    if (*front == EMPTY)
    {
        *front = *rear;
    }
 
    else
    {
        (tmp)->link = *rear;
    }
}
 
void dequeue(queue ** front, queue ** rear)
{
    queue * tmp;
    tmp = *front;
    *front = tmp->link;
    free(tmp);
}
 
int peek(queue ** front)
{
    queue *tmp;
    if (*front == EMPTY)
    {
        printf("Stack is Empty");
        return NULL;
    }
    return (*front)->data;
}
 
void main()
{
    queue * front = EMPTY;
    queue * rear = EMPTY;
    enqueue(&front, &rear, 10);
    enqueue(&front, &rear, 20);
    enqueue(&front, &rear, 30);
    enqueue(&front, &rear, 40);
 
    printf("%d\n", peek(&front));
    dequeue(&front, &rear);
    printf("%d\n", peek(&front));
    dequeue(&front, &rear);
    printf("%d\n", peek(&front));
    dequeue(&front, &rear);
    printf("%d\n", peek(&front));
}