Incorrect date value

[megha_3000]

i used the function on my php script

function dateconvert($date,$func){
  if ($func == 1){ //insert conversion
    list($day, $month, $year) = explode('[/.-]', $date);
    $year=trim($year);
	$date = "$year-$month-$day";
    return $date;
  }
  if ($func == 2){ //output conversion
    list($year, $month, $day) = explode('[-.]', $date);
    if(trim($date)!=='') $date = "$day/$month/$year";
    return $date;
  }
}

but at the time of execution it shows an error
: Incorrect date value: '--17-10-1989' for column 'dob' at row 1

the data type of dob is date default null.

how can i recover the error. help me. please give any suggestion.