Ask questions about the php variable scope ~~~

{Code...} Excuse me: I am listening to a php video from a teacher for 11 years, but the teacher's Code does not use static $ string. But no error is reported, but if I do not add static, the error will be reported, and the teacher will not use @. How can I define the variable so that it can be used in the function.

   function sub($str,$len){        for($i=0;$i<$len;$i++){            static $string;             if(ord(substr($str,$i,1))>0xa0){                  $string.=substr($str,$i,2);                   $i++;             }else                 $string.=substr($str,$i,1);             }        }        return $string;    }

Excuse me, I am listening to my 11-year php video from a teacher, but the teacher's code is not used.
Static $ string. But no error is reported, but if I do not add static, the error will be reported, and the teacher will not use @.
How can I define the variable so that it can be used in the function.

Reply content:

   function sub($str,$len){        for($i=0;$i<$len;$i++){            static $string;             if(ord(substr($str,$i,1))>0xa0){                  $string.=substr($str,$i,2);                   $i++;             }else                 $string.=substr($str,$i,1);             }        }        return $string;    }

Excuse me, I am listening to my 11-year php video from a teacher, but the teacher's code is not used.
Static $ string. But no error is reported, but if I do not add static, the error will be reported, and the teacher will not use @.
How can I define the variable so that it can be used in the function.

Use $ string as a parameter and do not need to add static. In this way, string is a global variable outside, and a local variable after passing in the function;
Then return the $ string, which makes the program clearer and easier to understand.

function sub($str,$len,$string){        for($i=0;$i<$len;$i++){             $string;             if(ord(substr($str,$i,1))>0xa0){                  $string.=substr($str,$i,2);                   $i++;             }else                 $string.=substr($str,$i,1);             }        }        return $string;    }

$ String =. I don't understand why static is used

The variables used in the function are global variables if they are not passed in.