Generating ramdom strings

[Elhombrebala]

I have this script that can generate a code and after it can check if it exists on DB, but in case code exists already:
¿How can I repeat the function till it finds a valid one?
I GUESS IS A BUCLE but, how to do it?

function RandomString($length=8) 
{ 
   //Generate alphabet array 
   $alphabet = ""; 
   for ($i = 0; $i < 26; $i++) { 
      @$alphabet .= chr(97+$i).","; 
   } 

   $alphabet = explode(",", $alphabet); 
   $RandomString = ""; 

   //Check that length is between 1 and 40 
   if ($length > 40 || $length < 1) { 
      $length = 8; 
   } 

   //Generate Random string 
   for ($i = 1; $i <= $length; $i++) { 
      $rand = rand(0, 25); 
      $RandomString .= $alphabet[$rand]; 
   } 

   return $RandomString; 
} 
$conexion=mysql_connect("","",""); 
mysql_select_db("database",$conexion);
$sql = mysql_query("SELECT * FROM Reservas WHERE codigo= '".RandomString()."'"); 
if (mysql_num_rows($sql) > 0) { 
      echo "RandomString is already taken"; 
} 
else { 
      echo "Not taken"; 
} 

[LordShryku]

You should move the check into the function. Then you can put a conditional in there that if it exists, try again, otherwise, return it

function RandomString($length=8) { 
   //Generate alphabet array
   $alphabet = ""; 
   for ($i = 0; $i < 26; $i++) { 
      @$alphabet .= chr(97+$i).","; 
   } 

   $alphabet = explode(",", $alphabet); 
   $RandomString = ""; 

   //Check that length is between 1 and 40
   if ($length > 40 || $length < 1) { 
      $length = 8; 
   } 

   //Generate Random string
   for ($i = 1; $i <= $length; $i++) { 
      $rand = rand(0, 25); 
      $RandomString .= $alphabet[$rand]; 
   } 

   $conexion=mysql_connect("","",""); 
   mysql_select_db("database",$conexion);
   $sql = mysql_query("SELECT * FROM Reservas WHERE codigo= '".$RandomString."'"); 
   if (mysql_num_rows($sql) > 0) { 
      RandomString();
   } 
   else { 
      return $RandomString; 
   }
}