Variables not working within Functions

Hi, I am starting to us functions with my work but I am having troubles With the variables in the functions.. If I have the following function called from my page it will work but the variable won’t ($username) but if I put this code straight on the page then it works fine.. Any reason for the variable not to work in the function but in straight coding? Thanx Sample Function Below: ====================================== function LoginSystem() { echo "<div align=right>"; if ( !isset( $_SESSION['login'] ) ) { echo "<form action=../Users/Login.php method=post>"; echo "<font size=1>Username: </font><input name=user type=text size=10>&nbsp;<font size=1>Password: </font><input name=pass type=password size=10>&nbsp;<input type=submit value=GO><br>"; echo "<a href=../Register.php><font size=1>Not A Member Yet?</font></font></a>&nbsp;"; echo "</form>"; } else { echo "<font size=1>Welcome $username &nbsp;&nbsp;&nbsp;<a href=../Users/Logout.php><font size=1>Logout</a>&nbsp;&nbsp;&nbsp;</font></font><br><br>"; } echo "</div>"; }