<?php

	class stack                      //定义一个栈的类

	{

		private $size;               //栈的空间大小

		private $top;                // 栈的指针

		private $stack_arr;          //栈的空间

		public function __construct($size)    //初始化一个空栈

		{

			$this->top=-1;

			$this->size=$size;

			$this->stack_arr=array();

		}

		public function push($data)           //入栈操作，先判断栈是否已满

		{

			if($this->top==$this->size-1)

				echo "The stack is full";

			else

				$this->stack_arr[++$this->top]=$data;

		}

		public function pop()               //出栈，取栈顶元素，先判断是否为空栈

		{

			if($this->top==-1)

				echo "The stack is empty";

			else

				return $this->stack_arr[$this->top--];

		}

		public function getlength()          //获取栈的大小

		{

			return $this->top+1;

		}

		public function print_stack()        //输出栈内元素

		{

			$tem=$this->top;

			while($tem!=-1)

			{

				echo $this->stack_arr[$tem--];

			}

		}

	}

	$stack=new stack(3);

	$stack->push('a');

	$stack->push('b');

	$stack->push('c');

	echo $stack->getlength();

	echo "<br/>";

	$stack->print_stack();

	echo "<br/>";

	echo $stack->pop();

	echo "<br/>";

	$stack->push('d');

	$stack->print_stack();

?>