php注册验证信息 求助啊·

<?
$username=$_POST['Enterprise_Name'];
$nc=$_POST['nc'];
$psw=$_POST['psw'];
$repsw=$_POST['repsw'];
$email=$_POST['email'];
function check()
{
    if($username=="")
    {
         echo"用户名不能为空";
         return false;
    } 

    if($nc=="")
    {
      echo"昵称不能为空";
      return false;
    }

    if($psw=="")
    {
      echo"密码不能为空";  
      return false;
    }
    if($repsw=="")
    {
      echo"密码确认不能为空";
      return false;
    }

    if($email != $_POST['repsw'])
    {
      echo"两次输入的密码不一致";
      return false;
    }

    if($email=="")
    {
      echo"邮箱不能为空";
      return false;
    }
      else return true;
    $year=$_POST['year'];
            if(($year%4==0&&$year%100!=0)||$year%400==0)
                 {
                 $two=29;
                 }
             else
                {
                 $two=28;
                }
            $yue=$_GET['months'];
            switch ($yue)
               {
                case 2:if($GET_['day']>two){echo"请输入正确的天数";return false;}break;
                case 4:
                case 6:
                case 9:
                case 11:
                       if($GET_['day']>30){echo"请输入正确的天数";return false;}break;
               }
     

}  
echo"恭喜您 注册成功！<br />";
echo"<a href='default.php'>返回<a>";
?>