栈的基本操作--插入，取栈顶元素，删除栈顶，清空栈

试了机组数据都对了。我忘了一部分c语言容错的语句了，没办法写得尽如人意。

#include<iostream>
#include<stdlib.h>
using namespace std;
struct stack{
	int size;
	int *top,*base;
};
stack a;
const int stacksize=10;
int top()
{
	int e;
	if(a.top==a.base)
		return -1;
	e=*(a.top-1);
	return e;
}
void insert(int e)
{
	if(a.top-a.base>=a.size)
	{
		a.base=(int*)realloc(a.base,(a.size+stacksize)*sizeof(int));
		a.top=a.base+a.size;
		a.size=a.size+stacksize;
	}
	*a.top=e;
	a.top=a.top+1;
}
void pop()
{
	if(a.top==a.base)
	{
		cout<<"error"<<endl;
		return;
	}
	a.top-=1;
}
void clear()
{
	while(a.top>a.base)
	{
		pop();
	}
}
int main()
{
	int n,i,traget,ko;
	a.size=stacksize;
	a.base=(int*)malloc(a.size*sizeof(int));
	a.top=a.base;
	cin>>n;
	for(i=1;i<=n;i++)
	{
		if(a.top-a.base>=a.size)
		{
			a.base=(int*)realloc(a.base,(a.size+stacksize)*sizeof(int));
			if(!a.base)
				exit(OVERFLOW);
			a.top=a.base+a.size;
		    a.size=a.size+stacksize;
		}
		cin>>*a.top;
		a.top=a.top+1;
	}
	cout<<top()<<endl;
	cin>>ko;
	insert(ko);
	cout<<top()<<endl;
	pop();
	cout<<top()<<endl;
	system("pause");
	return 0;
}