How to detect uppercase in a string

[impact]

Hello,

I have made a simple login script. In my script the username must be lowercase, Can some one please tell me how to detect presence of upper case in a string?

I tried doing this way but ...

$usernameLowerCase = strtolower($username);
if(strcoll($username, $usernameLowerCase) != 0){
// Show error
}

Any help will be appreciated. Thank you,

[enigma1]

Compare the converted with the original

if( $username != strtolower($username) ) {
// Not lower case
}

[impact]

Thank you,