@C语言数据结构大神：顺序栈求n!。13行的错误怎么修改？为啥说我定义栈错误？

Question

 # include<stdio.h>
# include<stdlib.h>
# define Max_Size 50
typedef struct{//typedef是小写开头! 
//注意此处的top是整形指针 
    int data[Max_Size];
    int top;
}SeqStack,*PSeqStack;


void Init_SeqStack(PSeqStack S)
{
    S->top=-1;//哪里错了？求解释！ 
}


int Full_SeqStack(PSeqStack S)
{
    if(S->top==Max_Size-1) return 1;
    else return 0;
}


int Empty_SeqStack(PSeqStack S)
{
    if(S->top==-1) return 1;
    else return 0;
}


void Push_SeqStack(PSeqStack S,int n)
{
    if(Full_SeqStack(S)==1) exit(0);

    else
    {S->top=++S->top;//及时先加一个空间 
     S->data[S->top]=n;}//栈也有data域！ 
}


void Pop_SeqStack(PSeqStack S,int n)//*n也是指针 
{   
    if(Empty_SeqStack(S)==1) printf("UnderFlow\n");

    else
     {n=S->data[S->top];
      S->top=--S->top;}//及时退一个空间 
}


int fact(int n,int f,PSeqStack S)//调用函数为什么不对?求解释！ 
{   
    Init_SeqStack(S);
    while(n!=0)
    {
    Push_SeqStack(S,n);
    n=n-1;
    }

    f=1;

    while(Empty_SeqStack(S)!=1)
    {
     Pop_SeqStack(S,n);
     f=f*n;
    }
    return f;
}


int main()
{   
    int n,f;SeqStack *S;
    printf("input n:\n");
    scanf("%d",&n);
    printf("%d\n",fact(n,f,S));

    getch();
}

Answer 1

int n,f;SeqStack *S;
->
int n,f;SeqStack *S = (SeqStack *)malloc(sizeof(SeqStack));