用php模拟一个简单的堆栈类

<?php
class stack{        
    private $top;        
    private $base;        
    private $myArr = array();        
    function __construct(){        
        $this->top = -1;        
        $this->base = -1;        
    }        
    function push($e){        
        $this->top++;        
        $this->myArr[$this->top] = $e;          
    }        
    function pop(){        
        if($this->top == -1){        
            echo '已经到了栈底！';        
        }else{        
            $this->top--;        
        }        
    }        
    function echoStack(){        
        for($i = 0; $i<=$this->top; $i++){        
            echo $this->myArr[$i] ;        
        }        
    }        
            
}        
$myStack = new stack();        
$myStack->push(100);        
$myStack->push(200);        
$myStack->push(300);        
$myStack->push(400);        
$myStack->echoStack();        
$myStack->pop();        
$myStack->echoStack();        
?>