title: How to undeclare (delete) variable in C?
body: <p>Like we do with macros:</p>
  
  <pre><code>#undef SOMEMACRO 
  </code></pre>
  
  <p>Can we also <em>undeclare</em> or <em>delete</em> the variables in C, so that we can save a lot of memory?</p>
  
  <p>I know about <code>malloc()</code> and <code>free()</code>, but I want to delete the variables completely so that if I use <code>printf("%d", a);</code> I should get error </p>
  
  <pre><code>test.c:4:14: error: ‘a’ undeclared (first use in this function)
  </code></pre>