 <p>Its not an error, It is a warning.</p> <p>It means that you have called the method <code>calculateTip()</code> which return Bool value. But you have not used this result anywhere.</p> <p>To suppress this warning just to this:</p> <pre><code>print(calculateTip()) </code></pre> <p>Now you are printing the output of the method, means the output is used now!</p>