title: How to prepare string variable format in flutter?
body: <p>I want to pass Roll_no to my rest API ?
  I want pass Roll_no like this format:</p>
  
  <pre><code>String roll_no = '3250$10';
  </code></pre>
  
  <p>How to prepare this format? 
  I have add $ between 3250 and 10 but it gives error like Expected an identifier.</p>