What am I doing wrong with these PHP session variables?

I created a signup/login system with PHP, and it works. Now I'm trying to have the index page display two images and two strings if the user is logged in. However, when I log in and go to the index page, it displays two broken image link icons and does not display either of the strings. I know I'm logged in, but I don't know why the following does not result in two images and two strings being displayed.

I am still learning PHP syntax. I tried different variations of single quotes vs. double quotes, and I tried writing the session variables into the HTML tags directly rather than assigning them to $a, $b, etc.

<?php
  session_start();
  include_once 'includes/database_connection.inc.php';
?>

<!DOCTYPE html>
<html>
  <head>
    <meta charset="utf-8">
    <link rel="stylesheet" href="css/1.css">
  </head>
  <body>
    <div id="div_name">
      <img id="index_logo" src="images/logo.jpg">
<?php
  if (isset($_SESSION['example_0'])) {
    $a = "images/folder 1/folder 2/" . $_SESSION['example_1'] . ".png";
    $b = "images/folder 1/folder 2/" . $_SESSION['example_2'] . ".png";
    $c = $_SESSION['example_3'];
    $d = $_SESSION['example_4'];
    echo '<img id="id_example_a" src="<?php echo $a; ?>">';
    echo '<img id="id_example_b" src="<?php echo $b; ?>">';                    
    echo '<p id="id_example_c"><?php echo $c; ?></p>';
    echo '<p id="id_example_d"><?php echo $d; ?></p>';           
  }
  else {
    echo '
      <a href="login.php">
        <button id="login_link_button">LOG IN</button>
      </a>
    ';
    echo '
      <a href="signup.php">
        <button id="signup_link_button">SIGN UP</button>
      </a>
    ';
  }
?>

Solution

You are echoing inside an echo

Assuming the session variables example_1 and example_2 contain valid and existing image names, then change to this - although I would style the link as a button instead of having a button in a link

<!DOCTYPE html>
<html>
  <head>
    <meta charset="utf-8">
    <link rel="stylesheet" href="css/1.css">
  </head>
  <body>
    <div id="div_name">
      <img id="index_logo" src="images/logo.jpg">
<?php
  if (isset($_SESSION['example_0'])) {
    $a = "images/folder 1/folder 2/" . $_SESSION['example_1'] . ".png";
    $b = "images/folder 1/folder 2/" . $_SESSION['example_2'] . ".png";
    $c = $_SESSION['example_3'];
    $d = $_SESSION['example_4'];
    ?>
    <img id="id_example_a" src="<?php echo $a; ?>">
    <img id="id_example_b" src="<?php echo $b; ?>">
    <p id="id_example_c"><?php echo $c; ?></p>
    <p id="id_example_d"><?php echo $d; ?></p>
<? } 
  else { ?>
     <a href="login.php">
        <button id="login_link_button">LOG IN</button>
      </a>
      <a href="signup.php">
        <button id="signup_link_button">SIGN UP</button>
      </a>
<? } ?>