为什么链栈一直是空栈，，看不出问题

Question

```c
//main.c

#include<stdio.h>
#include"LinkStack.h"
int main()
{
    LinkStack S;
    S=InitStack();
    for (int i = 0; i < 5; i++) {
        printf("数据;\n");
        int j = 0;
        scanf("%d", &j);
        Push(S, j);
    }
    int k=0;
    GetTop(S, &k);
    printf("栈顶;%d\n", k);
    Pop(S, &k);
    printf("出栈:%d\n", k);
    k = StackLength(S);
    printf("元素个数为;%d\n");
    PrintStack(S);
    return 0;
}


//LinkStack.c

#include<stdio.h>
#include<stdlib.h>
#include"LinkStack.h"
/*
#define OK 1
#define ERROR 2
typedef int Status;
typedef struct StackNode {
    int data;
    struct StackNode* next;
}StackNode, * LinkStack;
*/
LinkStack InitStack() {
    LinkStack S;
    S = (StackNode*)malloc(sizeof(StackNode));
    S = NULL;
    return S;
}
Status Push(LinkStack S, int e) {
    LinkStack p;
    p = (StackNode*)malloc(sizeof(StackNode));
    p->data = e;
    p->next = S;
    S = p;
    return OK;
}
Status Pop(LinkStack S, int* e) {
    if (S == NULL) {
        printf("空栈\n");
        return ERROR;
    }
    *e = S->data;
    LinkStack p = S;
    S = S->next;
    free(p);
    return OK;
}
Status GetTop(LinkStack S, int* e) {
    if (S != NULL) {
        *e = S->data;
        return OK;
    }
}
void DestroyStack(LinkStack S) {
    LinkStack p;
    while (S != NULL) {
        p = S->next;
        free(S);
        S = p;
    }
}
void ClearStack(LinkStack S) {
    LinkStack p,q;
    p = S->next;
    S = NULL;
    while (p != NULL) {
        q = p->next;
        free(q);
        p = q;
    }
}
int StackLength(LinkStack S) {
    if (S == NULL) {
        return ERROR;
    }
    LinkStack p = S;
    int cnt = 0;
    while (S != NULL) {
        cnt++;
        S = S->next;
    }
    return cnt;
}
void PrintStack(LinkStack S) {
    LinkStack p = S;
    while (p != NULL) {
        printf("%-3d", p->data);
        p = p->next;
    }
}




//LinkStack.h
#ifndef _LINKSTACK_H_
#define _LINKSTACK_H_
#define OK 1
#define ERROR 2
typedef int Status;
typedef struct StackNode {
    int data;
    struct StackNode* next;
}StackNode, * LinkStack;
LinkStack InitStack();
Status Push(LinkStack S, int e);
Status Pop(LinkStack S, int* e);
Status GetTop(LinkStack S, int* e);
void DestroyStack(LinkStack S);
void ClearStack(LinkStack S);
int StackLength(LinkStack S);
void PrintStack(LinkStack S);
#endif
@

```