title: Confusing about a very simple program
body: <p>I have this question :</p>
  <p><img src="https://i.stack.imgur.com/O9gAo.jpg" alt="enter image description here" /></p>
  <p>The program is very simple :</p>
  <pre><code>sub(b, a) 
  
  &lt;=&gt;
  
  sub(x, y) 
  x = x + y = 3 + 2 = 5 
  y = x + y = 5 + 2 = 7 
  
  &lt;=&gt; 
  b = 5
  a = 7 
  </code></pre>
  <p>therefore <strong>d</strong> is the right answer</p>
  <p>but the given answer is <strong>c</strong>(a = 7, b =3 )</p>
  <p>Why? What am i missing here ?</p>
  <p>Any help is greatly appreciated !</p>