title: C error: missing whitespace after the macro name
body: <p>I wrote the following macro:</p>
  
  <pre><code>#define m[a,b] m.values[m.rows*(a)+(b)]
  </code></pre>
  
  <p>However gcc gives me this error:</p>
  
  <pre><code>error: missing whitespace after the macro name
  </code></pre>
  
  <p>What is wrong and how do I fix it?</p>