php实现的计算器的例子，代码如下：

    
        
        
    
    $num1= true;
    $num2= true;
    $numa= true;
    $numb= true;
    $message= "";
     // 单路分支
     if(isset($_GET[ " sub "])){
         if($_GET[ " num1 "]== ""){
            $num1= false;
            $message.= " 第一个数不能为空 ";

        }
         if(!is_numeric($_GET[ " num1 "])){
            $numa= false;
            $message.= " 第一个数不是数字 ";
        }

         if($_GET[ " num2 "]== ""){
            $num2= false;
            $message.= " 第二个数不能为空 ";

        }
         if(!is_numeric($_GET[ " num2 "])){
            $numb= false;
            $message.= " 第二个数不是数字 ";
        }

         if($num1 && $num2 && $numa && $numb) {
            $sum= 0;
             // 多路分支switch
             switch($_GET[ " ysf "]){
                 case  " + ":
                    $sum=$_GET[ " num1 "]+$_GET[ " num2 "];
                     break;
                 case  " - ":
                    $sum=$_GET[ " num1 "]-$_GET[ " num2 "];
                     break;
                 case  " x ":
                    $sum=$_GET[ " num1 "]*$_GET[ " num2 "];
                     break;
                 case  " / ":
                    $sum=$_GET[ " num1 "]/$_GET[ " num2 "];
                     break;
                 case  " % ":
                    $sum=$_GET[ " num1 "]%$_GET[ " num2 "];
                     break;
            }
        }
    }
?>
Notice:  Undefined index:  num1  in 
D:\\php\\PHPnow1. 5.5\\Package\\vhosts\\ 127.0. 0.1\\ceshi\\jsq.php 
on line  64
    
        
            

计算器