#include <stdlib.h>

#define MIN_STACK_SIZE 1

struct stack_t{
  int length; 
  int top;
  char *array;
};

typedef struct stack_t * stack;

/*
 * create a empty stack according to the given len
 * return :the pointer to the stack
 */
stack Create_Stack(size_t len)
{
  if(len<MIN_STACK_SIZE)
  {
    return NULL;
  }

  stack s=(stack)malloc(sizeof(struct stack_t));
  if(s==NULL)
  {
    return NULL;
  }

  char *array=(char *)malloc(sizeof(char)*len);
  if(array==NULL)
  {
    return NULL;
  }

  s->top=-1;
  s->array=array;
  s->length=len;

  return s;
}

/* 
 * delete the given stack
 */
int Delete_Stack(stack s)
{
  if(s==NULL)
  {
    return -1;
  }

  free(s->array);

  free(s);
  return 1;

}
/*
 * return -1:empyt
 */
int IsEmptyStack(stack s)
{
  return s->top;
}

/*
 * push a char to stack s
 */
int Push_Stack(stack s,char c)
{
  if(s==NULL||s->top==(s->length-1))
  {
    return -1;
  }

  s->top++;

  s->array[s->top]=c;

  return 1;
}
/*
 * pop a char from stack s
 */
char Pop_Stack(stack s)
{
  if(s==NULL||s->top==-1)
  {
    return -1;
  }

  s->top--;

  return s->array[s->top+1];
}
/*
 * get a char from stack s
 */
char GetStackTop(stack s)
{
  if(s==NULL||s->top==-1)
  {
    return -1;
  }
  return s->array[s->top];
}