title: How to ask user input to call a method
body: <p>I want to make a simple calculator, so one that will calculate square meter, one that will calculate "pi" or anything you can imagine. But i want to call on the beginning of the running program, the calculator i want to use. so if i run the program, that the system will ask me if i want to use the calculator that calculates square meter or the pi.  for example output:</p>
  
  <ol>
  <li><strong>which calculator you want to use:</strong> SquareMeter</li>
  <li><strong>enter first number:</strong> 2</li>
  <li><strong>enter second number:</strong> 4</li>
  <li><strong>your answer is:</strong> 8</li>
  </ol>
  
  <p>My question is, how do i make this?</p>