title: Using #define in an "if" statement
body: <p>Is it possible to use <code>#define</code> in an "if" statement? The following code works, but I get a warning that the macro is being redefined.</p>
  
  <pre><code>if (UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiomPad) {
   #define TableViewHeight 916
   #define DisplayHeight 1024
   #define DisplayWidth 768
  }
  else {
   #define TableViewHeight 374
   #define DisplayHeight 480
   #define DisplayWidth 320
  }
  </code></pre>
  
  <p>I also tried this, but it didn't work:</p>
  
  <pre><code>#ifdef UIUserInterfaceIdiomPad
   #define TableViewHeight 916
   #define DisplayHeight 1024
   #define DisplayWidth 768
  #else
   #define TableViewHeight 374
   #define DisplayHeight 480
   #define DisplayWidth 320
  #endif
  </code></pre>
  
  <p>Any ideas?</p>