check string in c

what the fast way to check that string contain only characters within some set like "a-z0-9"?

>>74
Thanks Anonymous.

Here's the next iteration. I'm not sure about the return value though, it might need one more !.

is_inset(char*s){while(*s&(*s<'0'|*s>'9')&(*s<'a'|*s>'z'));return!*s;}

Next up is removing the extra set of parentheses.