链栈的入栈和出栈，求带神修改。

#include<stdio.h>
#include<stdlib.h>
#define NULL 0
typedef struct link
{
    int data;
    struct link *next;
}link;
int Bulid(link *s)
{
    s=NULL;
    return 1;
}
link *push(link *s)
{
    link *p;
    printf("Enter the value to push until -1 over:");
    for( ; ; ){
        p=(link * )malloc(sizeof(link));
        scanf("%d",&p->data);
    if(p->data==-1)
    {
        break;
    }
        p->next=s;
        s=p;
    }
    return s;
}
link *pop(link &s)
{
    link *temp;
    int num;
    if(s==NULL)
    {
        printf("Stack is Empty!");
    }
    else
    {
        num=s->data;
        temp=s;
        s=s->next;
        free(temp);
        printf("出栈元素为%d",num);
        return 1;

    }
}
void main()
{
    link *s;
    int k;
    char ch;
    do
    {
        printf("\n");
        printf("\n  1.初始化栈");
        printf("\n  2.入栈");
        printf("\n  3.出栈);
        printf("\n  0.结束");
        printf("\n==========================================");
        printf("\n  请输入你的选择(1,2,3,0)");
        scanf("%d",&k);
        switch(k)
        {
        case 1:{
                 Bulid(link &s);
               }break;
        case 2:{
            link *m;
               m=push(link &s);
               }break;
        case 3:{
                  pop(link &m);
               }break;
        }
        printf("\n-----------------------------------");
    }while(k>=1&&k<4);
    printf("\n          按回车键，返回...\n");
    ch=getchar();
}