title: decrement operator vs subtraction operator
body: <p>If I write a code like(in c)</p>
  
  <pre><code>    x=1;
      z=2;
      y=x---z;
  </code></pre>
  
  <p>will first two - be treated as post-decrement and later one as subtraction</p>
  
  <p>or first - will be treated as subtraction and other two as pre-decrement</p>
  
  <p>and what if I put a space to make it the other (because in  c program doesn't change by white space)</p>