废话少说，上代码(talk is easy,show me the code）:

<?php
  class SimpleStack {

  private $_stack = [];
  private $_size = [];

  public function __construct($size = 10)
  {
      $this->_size = $size;
  }

  // 获取栈顶元素
  public function pop()
  {
      // 空栈
      if (count($this->_stack) == 0) {
          return false;
      }
      return array_pop($this->_stack);
  }

  // 推送元素到栈顶
  public function push($value)
  {
      // 满栈
      if (count($this->_stack) == $this->_size) {
          return false;
      }
      array_push($this->_stack, $value);
      return true;
  }

  public function isEmpty()
  {
      // 是否是空栈
      return current($this->_stack) == false;
  }

  public function size()
  {
      return count($this->_stack);
  }
}

$stack = new SimpleStack(15);
var_dump($stack->isEmpty());  # true
$stack->push(111);
$stack->push('学院君');
var_dump($stack->pop());  # 学院君
var_dump(count($stack->size()));  # 1