/* stack1.c
 *
 * a stack implementation in C
 *
 * Jim Mahoney | cs.bennington.college | MIT License | March 2021
 */

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

#define STACK_SIZE 100

typedef struct _stack *stack;
struct _stack {
  int items[STACK_SIZE];
  int top;                // index of top of stack; -1 if empty
};

stack new_stack(){
  stack s = malloc(sizeof(struct _stack));
  s->top = -1;
  return s;
}

void free_stack(stack s){
  free(s);
}

void stack_push(int i, stack s){
  if (s->top < STACK_SIZE - 1){
    s->top++;
    s->items[s->top] = i;
  }
  else {
    printf("Error: exceeded max stack size\n");
    exit(-1);
  }
}

int stack_pop(stack s){
  s->top--;
  return s->items[s->top + 1];
}

int stack_peep(stack s){
  return s->items[s->top];  
}

int stack_is_empty(stack s){
  return s->top < 0;
}

int main(){
  stack s = new_stack();
  printf("push(1), push(2), then pop() until empty.\n");
  stack_push(1, s);
  stack_push(2, s);
  while (! stack_is_empty(s)){
    printf("%d\n", stack_pop(s));
  }
  return 0;
}