title: Difference between constant variables and global variables
body: <p>What is the difference between constant variables and global variables?</p>
  
  <pre><code>CONSTANT = 100
  $global = 100
  </code></pre>
  
  <p>I read this <a href="https://stackoverflow.com/questions/10778947/global-variable-vs-constant-vs-class-instance-variable-for-global-cache">question</a> but I can't understand.</p>