title: str_replace doesn't replace comma with dot
body: <p>I use str_replace but doesn't change the comma into a dot.</p>
  
  <pre><code>&lt;?php
  $hostname = "localhost"; 
  $username = "root";
  $password = "";
  $database = "grades";
  
  
  if(isset($_GET["herolist"]) &amp;&amp; isset($_GET["grade"]) &amp;&amp; isset($_GET["weight"])){
      $subject = $_GET["herolist"];
      $grade = $_GET["grade"];
      $weight = $_GET["weight"];
      str_replace(',', '.', $grade);
      echo $grade;
  }
  ?&gt;
  </code></pre>
  
  <p>I am really confused why it doesn't work because everywhere I look I see this option to replace a comma with a dot.</p>
  
  <p>Can someone maybe help me?</p>
  
  <p>Thanks!</p>