#include <stdio.h>
#include <stdlib.h>

#define TYPE int

typedef struct Node{
    TYPE data;
    Node *back;
}Node;

typedef struct Stack{
    Node *top;
}Stack;

void reset(Stack *s){ s->top = NULL; }
int isEmpty(Stack *s) { return !s->top; }

void push(Stack *s,TYPE val) {
    Node *node = (Node*) malloc(sizeof(Node));
    node->data = val;
    node->back = s->top;
    s->top = node;
}

TYPE pop(Stack *s) {
    if(!isEmpty(s)){
        Node *p = s->top;
        TYPE x = p->data;
        s->top = p->back;
        free(p);
        return x;
    }
}

void display(Stack s){ if(!isEmpty(&s)){ while(!isEmpty(&s)) printf(" {%d}\n",pop(&s) ); } }

int main(){
    Stack s; reset(&s);
    push(&s,5);
    push(&s,6);
    push(&s,7);
    display(s);
    display(s);
    return 0;
}