title: cap vs len of slice in golang
body: <p>What is the difference between cap and len of a slice in golang?</p>
  
  <p>According to definition:</p>
  
  <p>A slice has both a length and a capacity.</p>
  
  <p>The length of a slice is the number of elements it contains.</p>
  
  <p>The capacity of a slice is the number of elements in the underlying array, counting from the first element in the slice.</p>
  
  <pre><code>x := make([]int, 0, 5) // len(b)=0, cap(b)=5
  </code></pre>
  
  <p>Does the len mean non null values only?</p>