#include <stdio.h>
#include <stdlib.h>
void push(int);
int pop();

int *pi = NULL;//top指標
int *tos = NULL;//head指標

int main()
{
    int v;
    //申請50個int的空間
    pi = (int *)malloc(50*sizeof(int));
    if(!pi)
    {
        printf("allocation failure\n");
        exit(0);
    }
    tos = pi;
    do
    {
        printf("please input value, push it;enter 0 then pop;(enter -1 then stop)\n");
        scanf("%d", &v);
        if(v!=0)
            push(v);//加入空間
        else
            printf("pop this is it %d\n", pop());
    } while(v!=-1);

    free(tos);
}

void push(int i)
{
    pi++;
    if(pi==(tos+50))
    {
        printf("stack overflow\n");
        exit(0);
    }
    *pi = i;
}

int pop()
{
    if(pi==tos)
    {
        printf("stack underflow\n");
        exit(0);
    }
    pi--;
    return *(pi+1);
}