title: What does undefined : fmt.Println(build) means in GOlang? while using "fmt.Println(len("hello world")"
body: <p><img src="https://i.stack.imgur.com/GKFKn.png" alt="enter image description here"></p>
  
  <p>I am new to go language and programming.</p>
  
  <p>Can anyone explain what does the error means and how can I tackle it?</p>