PHP判断表达式中括号是否匹配的简单实例

<?php  
/ 
  title: 判断表达式中括号是否匹配 
  Description: () 匹配 )(不匹配 利用压栈和出栈 
  @author Mr Lv   

 /   
function isValid($expstr) { 
  $temp = array(); 
  for ($i=0; $i<strlen($expstr); $i++) { 
    $ch = $expstr[$i]; 
    switch($ch) { 
      case '(': 
        array_push($temp, '('); 
        break; 
      case ')': 
        if (empty($temp) || array_pop($temp) != '(') { 
          return "缺少左括号（"; 
        } 
    } 
  } 
  return empty($temp) == true ? "表达式匹配" : "缺少右括号）"; 
} 
$expstrA = "(1+3(64)-(2+3))()("; 
$expstrB = "(1+3(64)-(2+3))()"; 
$expstrC = "(1+3(64)-(2+3)))"; 
echo isValid($expstrA); 
echo "<br>"; 
echo isValid($expstrB); 
echo "<br>"; 
echo isValid($expstrC); 
?> 

缺少右括号） 
表达式匹配 
缺少左括号（