【栈】用链表

链表，队，栈在程序结束前都要注意有无释放表头结点。

 这个是带表头结点的，即head指针指向表头，表头中不存放数据，表头下一个指针指向第一个数据

包括

1. is_malloc_ok
2. create_node
3. create_stack
4. push_stack
5. pop_stack
6. is_empty
7. gettop_stack
8. empty_stack
9. release_stack

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


enum return_val {EMPTY_OK, EMPTY_NO, FULL_OK, FULL_NO, PUSH_OK, PUSH_NO, POP_OK, POP_NO, GET_OK, GET_NO};  
//没有size大小限制（因为是链表可以无限延伸），所以不用管is_full

struct stack_data
{
    int num;

    struct stack_data * next;
};

typedef struct stack_data Stack;

int is_malloc_ok(Stack *node)
{
    if(node == NULL)
    {
        return 0;
    }
    else
    {
        return 1;
    }
}

int create_node(Stack ** node)
{
    int count = 10;

    do
    {
        *node = (Stack*)malloc(sizeof(Stack));

        count--;

        if(count == 0)
        {
            printf("malloc error!\n");
            return 0;
        }

    }while(!is_malloc_ok(*node));

    return 1;

}



void create_stack(Stack ** head)
{
    
    if(create_node(head) == 0)
    {
        printf("创建失败！\n");
        exit(-1);
    }

    (*head)->next = NULL;
}

int push_stack(Stack * head,int num)
{
    Stack * node;

    create_node(&node);

    if(node == NULL)
    {
        return PUSH_NO;
    }
    else
    {
        node->num = num;
        node->next = head->next;
        head->next = node;
        return PUSH_OK;
    }
}

int pop_stack(Stack *head,int * num)
{
    Stack *p;

    if(is_empty(head) == EMPTY_OK)
    {
        printf("stack is empty!\n");
        return POP_NO;
    }
    else
    {
        *num = head->next->num;
        p = head->next;
        head->next = head->next->next;
        free(p);
        return POP_OK;
    }
}

int is_empty(Stack *head)
{
    if(head->next == NULL)
    {
        return EMPTY_OK;
    }
    else
    {
        return EMPTY_NO;
    }
}

int gettop_stack(Stack *head, int *num)
{
    if(is_empty(head) == EMPTY_OK)
    {
        printf("stack is empty!\n");
        return GET_NO;
    }
    else
    {
        *num = head->next->num;
        return GET_OK;
    }

}

void empty_stack(Stack *head)
{
    Stack * p = head;

    while(head->next != NULL)
    {
        p = head->next;
        head->next = p->next;
        free(p);
    }
}

void release_stack(Stack **head)
{
    Stack *p;

    empty_stack(*head);

    p = *head;
    *head = NULL;
    free(p);

}

int main()
{
    Stack * head;
    int i;
    int num;

    create_stack(&head);

    for(i = 0; i < 10; i++)
    {
        if(push_stack(head,i + 1) == PUSH_NO)
        {
            printf("push no!\n");
        }
        else
        {
            printf("push ok! num is %d\n",i + 1);
        }
    }

    for(i = 0; i < 7; i++)
    {
        if(pop_stack(head,&num) == POP_NO)
        {
            printf("pop no!\n");
        }
        else
        {
            printf("stack is %d\n",num);
        }
    }

    empty_stack(head);

    for(i = 0; i < 5; i++)
    {
        if(gettop_stack(head,&num) == GET_NO)
        {
            printf("gettop no!\n");
        }
        else
        {
            printf("top is %d\n",num);
            pop_stack(head,&num);
        }
    }

    release_stack(&head);

    return 0;

}

 小练：

改进要点：

1. 要学会用老师的enum系列
2. 没写is_malloc_ok系列
3. empty没写，只写了release stack函数
4. 缺少一些提示，比如栈空了要说“栈已空”之类
5. GetTop最好按老师的写，int GetTop(Stack *head,int *num);这样比较好，不然return谁知道你返回的是不是top值还是错误（我返回的是NULL不太好）

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

struct stack_data
{
	int num;
	struct stack_data *next;
};

typedef struct stack_data Stack;

int CreateNode(Stack **s)
{
	*s = (Stack *)malloc(sizeof(Stack));
	if(*s == NULL)
	{
		return 0;
	}
	return 1;
}

int CreateStack(Stack **s)
{
	if(!CreateNode(s))
		return 0;
	(*s)->next = NULL;
	return 1;
}

int IsEmpty(Stack *s)
{
	if(s->next == NULL)
		return 1;
	return 0;
}

int Pop(Stack *s,int *num)
{
	Stack *p;

	if(IsEmpty(s))
		return 0;

	*num = s->next->num;
	p = s->next;
	s->next = s->next->next;
	free(p);
	return 1;
}

int Push(Stack *s,const int num)
{
	Stack *p;

	if(!CreateNode(&p))
		return 0;
	p->num = num;
	p->next = s->next;
	s->next = p;
	return 1;
}

//改进！
int GetTop(Stack *s)
{
	if(IsEmpty(s))
	{
		printf("Link is empty\n");
		return NULL;
	}
	return s->next->num;
}

//我写的相当于release版本
void MakeEmpty(Stack **s)
{
	int num;

	while(!IsEmpty(*s))
		Pop(*s,num);

	free(*s);
	*s = NULL;
}

int main()
{
	Stack *head;
	int i, num;

	CreateStack(&head);

	i = 0;
	num = 1;
	while(i < 10 && Push(head,num))
	{
		i++;
		num++;
		printf("%d\n",GetTop(head));
	}

	printf("----------------------\n");

	while(Pop(head,&num))
	{
		printf("%d\n",num);
	}

	MakeEmpty(&head);
	return 0;
}