Notice: Uninitialized string offset in PHP -

Hello, I have this function and it returns a notice:

Notice: Unscrupited string offsets:

function generator and $ ($ length) {$ string = ''; $ Letters = "0123456789abcdef"; ($ P = 0; $ p & lt; $ length; $ p ++) {$ string = $ Letters [mt_rand (0, strlen ($ letters)); } Return $ string; }

The affected line is:

  $ string. = $ Letters [mt_rand (0, strlen ($ letters)];   
 I have tried to do with braces and it does not work. If someone can tell some suggestion, then I appreciate it. Thank you.  
  
 
 
 You can sometimes sometimes overwrite due to  $ letter  strlen ($ Character) , which should be  strlen ($ letters) - 1 . Your random series should start with zero, and you have to end with  a zero  length if the  $ character  is 10, then the last zero-based array index < Em> nine , and it keeps up your upper limit for random selection.  
  $ string = ''; $ Letters = "0123456789abcdef"; ($ P = 0; $ p & lt; $ length; $ p ++) {$ string = $ Characters [mt_rand (0, strlen ($ letters) - 1)]; }   
 Because you are randomly selected, you do not always get the information - it only happens when  mt_rand ()  returns its maximum value at any point In your loop