title: "cc1: error: /usr/local/include: not a directory" after installing C library
body: <p>This is the first time I install a library. I followed the instructions <a href="http://cdn.cs50.net/2010/fall/lectures/2/src/cs50.h" rel="nofollow">here</a>. It's from an online course on programming. </p>
  
  <p>I'm not very Unix savvy. When I tried to compile one of the sample c files, one that #includes the cs50.h file, I get:</p>
  
  <pre><code>cc1: error: /usr/local/include: not a directory
  </code></pre>
  
  <p>Also, if I write <code>cd /usr/local/include</code> or <code>cd /usr/local/lib</code>, it tells me it's not a directory again, even though when I <code>ls /usr/local</code> they both show up. </p>
  
  <p>Any ideas?</p>