title: pass a value to another c file
body: <p>I have a <code>A.c</code> file that contains some <code>char*</code> variable <code>str1</code>.
  I have a <code>B.c</code> file that contains some <code>f()</code> function, that make some transformation on a <code>char*</code> variable.</p>
  
  <p>My point is: How can I pass the value of <code>str</code> to <code>B.c</code>, then compute the new string thanks to <code>f()</code>, and afterwards send back the new string value to <code>A.c</code> ?</p>