trim function to remove blank spaces and verify that the value is not an EMPTY word

<?php
session_start();
$word1 = htmlspecialchars($_SESSION['word'][1]);
$word2 = htmlspecialchars($_SESSION['word'][2]);
$word3 = htmlspecialchars($_SESSION['word'][3]);
$word4 = htmlspecialchars($_SESSION['word'][4]);
$word5 = htmlspecialchars($_SESSION['word'][5]);

if (isset($_SESSION['word'][1]) && isset($_SESSION['word'][2]) && isset($_SESSION['word'][3]) && isset($_SESSION['word'][4]) && isset($_SESSION['word'][5]) ) {

  for($i = 1; $i <= 5; $i++) {
   if (strlen($str) > 0 && strlen(trim($str)) == 0) {
      header('Location: play.php?p=');
    }
   $_SESSION['word'][i] = str_replace(' ', '', $string);
   empty($_SESSION['word'][i]);
  }

include 'inc/header.php';

echo '<h1>My Treehouse Story</h1>';

echo '<p>There once was a(n) ' . $word1;
echo ' programmer named ' . $word2; 
echo '. </p>';
echo '<p>This ' .  $word3; 
echo ' programmer used Treehouse to learn to ' . $word4;
echo ' the ' . $word5 . '.</p>';

echo ' <a class="btn btn-default btn-lg" href="#" role="button">Save Story</a>';
echo ' <a class="btn btn-default btn-lg" href="play.php" role="button">Play Again</a>';
echo ' <a class="btn btn-default btn-lg" href="index.php" role="button">Other Stories</a>';


include 'inc/footer.php'; 
} else {
 if (empty($_SESSION['word'][1])) {
 header('Location: play.php?p=1');
 } else if (empty($_SESSION['word'][2])) {
 header('Location: play.php?$p=2');
 } else if (empty($_SESSION['word'][3])) {
 header('Location: play.php?p=3');
 } else if (empty($_SESSION['word'][4])) {
 header('Location: play.php?p=4');
 } else if (empty($_SESSION['word'][5])){
   header('Location: play.php?p=5');
 }
}

for ($word = 1; $word <= 5; $word++) {
  $trimmed = trim($_SESSION['word'][$word]);
  if (empty($trimmed)) {
    if ($word == 1) {
      header('location:play.php');
      exit;
    } else {
      header('location:play.php?p='.$word);
      exit;
    }
  }
}