title: Use of operator ()
body: <p>I have few question about <code>()</code> operator. Please help me  to get clear idea.</p>
  
  <ol>
  <li>What is the use of <code>()</code> operator (<code>()</code> operator overloading).</li>
  <li>In which situations it should use.</li>
  <li>What are the  practical example of <code>()</code> operator usage (in which situations that useful,convenient or suitable to use <code>()</code> operator ).</li>
  </ol>