stack栈入门

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


struct node_st {
int data;
struct node_st *next;
};


static struct node_st *list = NULL;


static int is_empty(void)
{
if (list == NULL) {
return 1;
}
return 0;
}


static int is_full(void)
{
return 0;
}


int push(int data)
{
struct node_st *newnode;


if (is_full()) {
return -1;
}


newnode = malloc(sizeof(*newnode));
/* if error */


newnode->data = data;
newnode->next = list;
list = newnode;


return 0;
}


int pop(int *data)
{
struct node_st *save;


if (is_empty()) {
return -1;
}


*data = list->data;
save = list;
list = save->next;
free(save);


return 0;
}


int main(void)
{
int arr[] = {3,2,1,6,7};
int i;
int data;
int ret;


for (i = 0; i < sizeof(arr) / sizeof(*arr); i++) {
ret = push(arr[i]);
if (ret == -1) {
printf("stack full.\n");
break;
}
}


while (1) {
ret = pop(&data);
if (ret == -1) {
printf("stack empty.\n");
break;
}
printf("%d ", data);
}
printf("\n");


return 0;
}