title: Initializer must be constant
body: <p>I am trying to learn C but I get an error in the following code.<br><br>
  If I use <strong>radius</strong> in volume I get an error: <code>error #2069: Initializer must be constant.</code></p>
  
  <pre><code>#include &lt;stdio.h&gt;
  #define PI (3.14)
  
  /* Define radius*/
  int radius = 10;
  float volume = ( 4.0f / (3.0f * PI * radius) );
  
  int main(void){
  
  return 0;
  }
  </code></pre>
  
  <p>But when I change radius with an actual number, it compiles just fine.</p>
  
  <pre><code>#include &lt;stdio.h&gt;
  #define PI (3.14)
  
  /* Define radius*/
  int radius = 10;
  float volume = ( 4.0f / (3.0f * PI * 10) );
  
  int main(void){
  
      return 0;
  }
  </code></pre>
  
  <p>Why does this happen, and what can I do to make the first version work?</p>