How can I prevent people from using a email address as a username. I only want letters as username. No symbles at all...
Only letters? Normally, usernames are allowed to consist of letters or numbers. In this case, you could use [man]ctype_alnum/man to validate their input.
If you truly only wanted letters, though, you could use [man]ctype_alpha/man.
OK so if i want them to use letters and numbers and underscore how would I check to make sure that is what they use and no other symbles
For that... I would make your own regexp:
if(preg_match('/[^a-z0-9_]/i', $username)) { // invalid chars }
