php - how to make static variable initialize to global variable -

the problem want change value of global variable each time sub called ,how can possibly it

         function sub()              {            static $x=global $present;             static $y=global $max;             static $z=global $min;         if($x==$z)         {      $x=$y;              }             $x--;            return $x;                }              sub();              sub();               sub(); 

i have tried too

          function sub()              {             global $present;             global $max;             global $min;         if($present==$min)         {      $present=$max;              }             $present--;            return $present;                }                sub();//it works once               sub();               sub(); 

please provide me solution can change value of global variable each time function called.......thank you

the main function of sub retrieving value frm data base ,src remains same no matter how many times call change function please me out

         function sub()               { global $present; global $max; global $min;        if($present==$min)         { $present=$max;           }           else            --$present;          return $present;                  }                  <script>             function change()                   {                      alert("hello");                  var x=document.getelementbyid("show");        x.src='<?php             if($con==true)             {        $cmd="select * showcase item_no=".sub();            if($res=$con->query($cmd))               {       if($res->num_rows>0)             {           while($rw=$res->fetch_array())            {             echo "$rw[1]";                 }                  }      else       {      echo "no record found";         }          }         else   {        echo "query problem";       }}             ?>';               alert(x.src);                      }                   </script> 

this code works me:

<?php  $x = 5;  function sub() {     global $x;      --$x; }  sub(); var_dump($x); sub(); var_dump($x); sub(); var_dump($x); sub(); var_dump($x); 

output 4, 3, 2, 1. see yourself: http://3v4l.org/tic1v