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栈作为一种简单但常用的数据结构，要想完全正确的实现还是需要经过一番考虑的。《剑指offer》这本书一再强调代码的鲁棒性。

下面是一个栈的简单c语言实现，作为一个学习过程记录如下。

#include <stdio.h>
#include <stdlib.h>int gError = 0; //用于栈为空时，仍弹栈的标记
typedef struct Node {
int data;
struct Node* next;
} Node ;
int length(Node*);
void push(Node** stack,const int a)
{if(*stack==NULL){*stack = (Node*)malloc(sizeof(Node));(*stack)->data = a;(*stack)->next = NULL;} else {Node* p = *stack;int len = length(p);for(int i=0;i<len-1;i++){p = p->next;}p->next = (Node*)malloc(sizeof(Node));p->next->data = a;p->next->next = NULL;}
}
int length(Node* head)
{Node* p = head;int count = 0;while(p!=NULL){p = p->next;count++;}return count;
}
int pop(Node** head)
{if(*head==NULL){fprintf(stdout,"null stack\n");gError = 1;return -1;}Node* p = *head;int len = length(p);int tmp = 0;Node* prev = NULL;if(len==1){tmp = p->data;free(p);*head = NULL;} else {for(int i=0;i<len-1;i++){prev = p;p = p->next;}prev->next = NULL;tmp = p->data;free(p);}return tmp;
}
void  print(Node* head)
{Node* p = head;while(p!=NULL){fprintf(stdout,"%3d",p->data);p = p->next;}
}int main(void)
{Node* head = NULL;push(&head,13);push(&head,14);push(&head,15);push(&head,16);print(head);printf("\n");printf("top is : %d\n",pop(&head));printf("top is : %d\n",pop(&head));printf("top is : %d\n",pop(&head));printf("top is : %d\n",pop(&head));return 0;
}