Trying to create a log in system but getting error “Parse error: syntax error, unexpected ‘else’ (T_ELSE) ” [closed]

That code looks completely mangled. Try:

if (!filter_var($email, FILTER_VALIDATE_EMAIL)) {
   header("Location: ../signup.php?error=invalidmail&uid=" . $username);
   exit();
}

Count up the if and else and make sure they surround the code correctly. Although you can skip the {} when using a single line of code, it’s good practice to always add them in, so you can avoid messy, error prone code like this.

if($value = 10) {
   // Your code
} else {
   // Something else
}

Finally, this isn’t anything to do with WordPress.