title: Error when compiling with GCC
body: <p>Every time I compile I get the following error message:</p>
  
  <pre><code>Undefined reference to ( function name )
  </code></pre>
  
  <p>Let's say I have three files: <code>Main.c</code>, <code>printhello.h</code>, <code>printhello.c</code>. <code>Main.c</code> calls function <code>print_hello()</code>, which returns "Hello World". The function is defined in <code>printhello.c</code>.</p>
  
  <p>Now, here's the following code of printhello.h:</p>
  
  <pre><code>#ifndef PRINTHELLO_H 
  #define PRINTHELLO_H
  
  void print_hello();
  
  #endif
  </code></pre>
  
  <p>I am sure this code is fine. I still don't know why is it giving me the error, though. Can you help me?</p>