php无法正常使用html

Question

<?php
  if(!isset($_SESSION['c_id']) || (!isset($_SESSION['s_id'])))
  {
  ?>
  Login/Register
  <ul>
  <li>
  <a href="register.php">
  Student Login
  </a>
  </li>
  <li>
  <a href="register.php">
  Student Registration
  </a>
  </li>
  <li>
  <a href="company_register.php"">
  Company Login
  </a>
  </li>
  <li>
  <a href="company_register.php">
  Company Registration
  </a>
  </li>
  </ul>
  </li>
  <?php
  } 
  else
  {
  ?>
  <a href="logout_exec.php>Logout
  </a>
  </li>
  <?php
  }
  ?>
  </ul>

This is my code snippet,

When the user is logged in, even then Logoutis not being displayed, as clear from the post if the SESSION IDs are not set means the user is not logged in, in that case the content pertaining to that condition is being displayed however not the other way round

The login_exec.php file

include ("db_conn.php");

function clean_input($data)
{
$data = stripslashes($data);
$data = trim($data);
$data = htmlspecialchars($data);
return $data;
}
//registration form data validation

if(!empty($_POST['Go']))
{
$email= $password= "";
$email= clean_input($_POST['email']);
$pass= clean_input($_POST['pass']);
$pass = hash("sha256", $pass);
$type= $_GET['type'];

global $query;

if($type=="student")
{
$query= "SELECT * FROM STUDENT WHERE email='$email' AND password='$pass'";
}

elseif($type=="company")
{
$query= "SELECT * FROM COMPANY WHERE email='$email' AND password='$pass'";
}
echo $query;
$query1= mysqli_query($dbhandle,$query);
if(!$query1)
{
echo 'MySQL Error: ' . mysqli_error();
        exit;
        }

$count= mysqli_num_rows($query1);

if($count==0)
{echo "No Data";
}
else
{
while($row=mysqli_fetch_assoc($query1))
if($type=="student")
{

session_start();
$_SESSION['sname']= $row['F_Name'].' '.$row['L_Name'];
$_SESSION['s_id']= $row['id'];
header('Location: /Internshala/index.php?s_id='.$_SESSION['s_id']);

}
elseif($type=="company")
{
session_start();
$_SESSION['cname']=$row['Name'];
echo $_SESSION['cname'];
$_SESSION['c_id']=$row['c_id'];
header('Location: /Internshala/index.php?c_id='.$_SESSION['c_id']);
}
}
}

Answer 1

Finally...

If using OR operator , then even if one of the SESSION variables are not set, the script will display everything except else's block.

And even after using the AND operator when Coding Horror suggested that the if(condition) is wrong, it won't work. But while discussing with Fred ii, I noticed the mismatch between <?php and ?> towards the end, which finally made me discover a missing " here <a href="logout_exec.php>Logout. So this was the reason for the havoc.

All help is much appreciated.