变量变量在PHP中的IF语句中定时输出

I am trying to set some dynamic variables to NULL to avoid the "Warning: Undefined variable" warning. I am using this piece of code:

        $i = 1;
        while($i <= 15){
            if(!isset(${"ss".$i})){
            ${"ss".$i} = null;
            $i = $i + 1;
            }
        }

However, it just times out at 60 seconds Fatal error: Maximum execution time of 60 seconds exceeded in /www/sites/164/edit.php on line 94

Any idea why this is happening?

You only increase $i inside the IF statement. If the IF is false, it'll be trapped in an infinite loop.

You're getting in infinite loop. Change your code to:

$i = 1;
while($i <= 15) {
   if(!isset(${"ss".$i})){
      ${"ss".$i} = null;
   }
   $i = $i + 1;
}

I suggest you use Error Control Operators to suppress the warnings instead of having to run that loop every time.