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link.h

#ifndef LINKEDLIST_H
#define LINKEDLIST_H

typedef struct node *link;

struct node
{
?unsigned char item;
?link next;
};

link make_node(unsigned char item);
void free_node(link p);
link search(unsigned char key);
void insert(link p);
link delete(link p);
void traverse(void(*visit)(link));
void destroy(void);
void push(link p);
link pop(void);

#endif

?

link.c

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

static link head = NULL;

link make_node(unsigned char item)
{
?link p=malloc(sizeof *p);
?p->item = item;
?p->next = NULL;
?return p;
}

void free_node(link p)
{
?free(p);
}

link search(unsigned char key)
{
?link p;
?for (p=head;p;p=p->next)
??if (p->item == key)
???return p;
?return NULL;
}

void insert(link p)
{
?p->next=head;
?head=p;
}

link delete(link p)
{
?link prev;
?if (p==head)
?{
??head=p->next;
??return p;
?}
?for (prev=head;prev;prev=prev->next)
??if (prev->next == p)
??{
???prev->next=p->next;
???return p;
??}
?return NULL;
}

void traverse(void (*visit)(link))
{
?link p;
?for(p=head;p;p=p->next)
??visit(p);
}

void destroy(void)
{
?link q, p=head;
?head=NULL;
?while(p)
?{
??q=p;
??p=p->next;
??free(q);
?}
}

void push(link p)
{
?insert(p);
}

link pop(void)
{
?if (head==NULL)
??return NULL;
?else
??return delete(head);
}

void printf_item(link p)
{
?printf("%d\n",p->item);
}
int main(void)
{
??? link p=make_node(10);
??? insert(p);
??? p=make_node(5);
??? insert(p);
??? p=make_node(90);
??? insert(p);
??? p=search(5);
??? delete(p);
??? free_node(p);
??? traverse(printf_item);
??? destroy();

??? p=make_node(100);
??? push(p);
??? p=make_node(200);
??? push(p);
??? p=make_node(220);
??? push(p);
??? while(p=pop())
??? {
??????? printf_item(p);
??????? free_node(p);
??? }
??? return 0;
}