Paste code

<html>
   <head>
    <title>
     Assignment</title>
      <link rel="stylesheet" type="text/css" href="v.css" />
      </head>
        <body>
    <form name="form" acti method="POST">
     <div id="main">
       <h1><Registration</h1>
        <table>
         <tr>
           <td id="firstcol">Username:</td>
            <td><input type="text" name="username" value="<?php if(isset($_POST['submit']))echo $_POST['username']?>"/></td>
              <td><span id="error_username" class="error">
<?php 
      if(isset($_POST['submit']))
       {
        $username=$_POST['username'];
        if(trim($username)=="")
          {
          echo"field cannot be black";
           }
          else if($username)<8||strlen($username)>12)
           {
           echo "only 8 to 12 ";
           }
           }
     
?>
</span></td></tr></table>
<input type="submit" name="submit" value="submit"/>
<?php
if(isset($_POST['submit']))
{
echo "username";
$_POST["username"]."<br/>";
}
?>

</div>
</body>
</html>