c语言 链表实现堆栈

不知道怎么得到栈顶指针

#include <stdio.h>
#include <stdlib.h>
typedef struct Stack{
	int elem;
	struct Stack *next;
}stack;
//初始化
stack* init(){
	stack *s=(stack*)malloc(sizeof(stack));
	s->elem=NULL;
	s->next=NULL;
	return s;
} 
//压栈
stack* push(stack *s,int val){
	stack *a=(stack*)malloc(sizeof(stack));
	a->elem=val;
	a->next=s->next;
	s->next=a;
} 
//出栈
int pop(stack *s){
	stack *t;
	t=s->next;
	s->next=s->next->next;
	printf("%d  ",t->elem);
	return  t->elem	;
} 
int main(){
	stack *s= init();
	push(s,1);
	push(s,2);
	pop(s);
	pop(s);
	return 0;
}