Hàm PHP chữ hoa sang chữ thường và ngược lại

 #### mb_convert_case

$str = "mary had a Little lamb and she loved it so";

$str = mb_convert_case($str, MB_CASE_UPPER, "UTF-8");

echo $str; // Prints MARY HAD A LITTLE LAMB AND SHE LOVED IT SO

$str = mb_convert_case($str, MB_CASE_TITLE, "UTF-8");

echo $str; // Prints Mary Had A Little Lamb And She Loved It So

#### mb_ucfirst

function mb_ucfirst($str, $encoding = "UTF-8", $lower_str_end = true) {

$first_letter = mb_strtoupper(mb_substr($str, 0, 1, $encoding), $encoding);

$str_end = "";

if ($lower_str_end) {

$str_end = mb_strtolower(mb_substr($str, 1, mb_strlen($str, $encoding), $encoding), $encoding);

}

else {

$str_end = mb_substr($str, 1, mb_strlen($str, $encoding), $encoding);

}

$str = $first_letter . $str_end;

return $str;

}