栈

前面我们讲到了容器，今天我们接着讨论另外一种数据结构：
堆栈。堆栈几乎是程序设计的命脉，没有堆栈就没有函数调用，当然也就没有软件设计。

那么堆栈有什么特殊的属性呢？其实，堆栈的属性主要表现在下面两个方面：

1）堆栈的数据是先入后出

2）堆栈的长度取决于栈顶的高度

那么，作为连续内存类型的堆栈应该怎么设计呢？大家可以自己先试一下：

#ifndef _stack_h
#define _stack_h

#include <stdio.h>
#include <stdlib.h>
#define EMPTYSTACK -1
#define MINSTACKSIZE 5

typedef struct stackRecord
{
     int capacity;
     int topOfStack;
     void **array;
}*stack;
//stack s ==> struct stackRecord * s;
int isEmpty(stack s);
int isFull(stack s);

stack createStack(int maxElementsNumber);
void disposeStack(stack s);
int push(void *e, stack s);
void *top_element(stack s);
int pop(stack s);
void *topAndPop(stack s);
int getStackLength(stack s);

#endif

#include "stack.h"

int main(int argv, char *argc[])
{
     stack s;
     s = createStack(5);
     push((void *)5, s);
     printf("The Stack's length is %d\n", getStackLength(s));

     push((void *)6, s);
     printf("The Stack's length is %d\n", getStackLength(s));

     printf("The top element is %d\n", (int)top_element(s));
     pop(s);

     printf("The Stack's length is %d\n", getStackLength(s));
     pop(s);
    // pop(s);
    // disposeStack(s);
     pop(s);
     push((void*)8,s);
     printf("The top element is %d\n", (int)top_element(s));
     return 0;
}

int isEmpty(stack s)
{
　　return s->topOfStack == EMPTYSTACK;
}

int isFull(stack s)
{
　　return (s->topOfStack + 1) == s->capacity;
}
void disposeStack(stack s)
{
    s->topOfStack = -1;

    if (s != NULL) {
        free(*s->array);
        *s->array = NULL;
        free(s->array);
        s->array = NULL;
   //   free(s);
    }
}

stack createStack(int maxElements)
{
    stack s = (stack)malloc(sizeof(struct stackRecord));

    if (maxElements < MINSTACKSIZE)
        perror("Stack size is too small.");
    if (s == NULL)
        perror("Out of space!");

    s->array = (void **)malloc(sizeof(void *) * maxElements);
    s->capacity = maxElements;
    s->topOfStack = -1;

    return s;
}

int push(void *e, stack s)
{
    if (!isFull(s))
    {
        s->array[++s->topOfStack] = e;
        return 0;
    }
    else
        return 1;
}

/* when the stack is empty it'll return 0 */
void *top_element(stack s)
{
      if (!isEmpty(s))
            return s->array[s->topOfStack];
      else
            return NULL;
}

int pop(stack s)
{
    if (!isEmpty(s))
    {
        s->array[s->topOfStack--] = '\0';
        return 0;
    }
    else
    {
        printf("it is empty !\n");
        return 1;
    }
}

void *topAndPop(stack s)
{
 　　void *e;
  　  e = top_element(s);
 　   pop(s);
  　  return e;
}
int getStackLength(stack s)
{
　　return (s->topOfStack+1) ;
}