求各位解答，求正确方法

为什么我的代码在vc++6.0一直说'top' is not a member of 'node'

typedef struct node{
char info;
struct node *link;
} STACK;
STACK *top;
push(arg)
char arg; {
STACK *ptr;
ptr=(STACK *)malloc(sizeof(STACK));
ptr->info=arg;
ptr->link=top;
top=ptr; }
char pop()
{ STACK *ptr;
char arg;
if(top=='\0')
return('\0');
else{
ptr=top;
top=top->link;
arg=ptr->info;
free(ptr);
return(arg); } }
main()
{STACK *s1;
int n,dt;
s1.top=0;
printf("Input a decimal number:");
scanf("%d",&n);
while( n != 0){
push(&s1,n%8);
n=n/8; }
printf("The octal number is:");
while((dt=pop(&s1))!= -1)
printf("%d",dt);
printf("\n"); }

修改处见注释，供参考：

#include <stdio.h>
#include <stdlib.h>
typedef struct node{
    int    info;   //char info
    struct node *link;
} STACK;
                   //STACK *top;
void push(STACK**top,int arg) //修改
{
    STACK *ptr;
    ptr=(STACK *)malloc(sizeof(STACK));
    ptr->link = NULL;
    ptr->info=arg;
    ptr->link=(*top);        //修改
    (*top)=ptr;              //修改
}
int pop(STACK**top)    //char pop() //修改
{
    STACK *ptr;
    int arg;           //char arg;
    if((*top) == NULL) //if(top=='\0')
       return -1;      //return('\0');
    else{
       ptr=(*top);     //修改
       (*top)=(*top)->link;//修改
       arg=ptr->info;
       free(ptr);
       return(arg);
    }
}
int main()
{
    STACK *s1 = NULL;
    int n,dt;
                        //s1.top=0;
    printf("Input a decimal number:");
    scanf("%d",&n);
    while( n != 0){
          push(&s1,n%8);
          n=n/8;
    }
    printf("The octal number is:");
    while((dt=pop(&s1))!= -1)
          printf("%d",dt);
    printf("\n");

    return 0;
}

换个运行环境