title: Use once on arc4random() number
body: <p>How you code arc4random() that does not repeat number twice? </p>
  
  <p>For instance. I'm using switch and button. I don't want to generate reused the same arc4random number again. If I have arc4random that generation numbers 2,4,42,32,42...
  I don't want to 42 to appear again. </p>
  
  <p>How do I avoid this?</p>
  
  <pre><code>  switch (arc4random() % 50 )
          {
              case 1:
                  text.text = @"You are silly boy";
                  break;
              case 2:
                  text.text = @"Well, you very very silly"];
                  break;
              case 3:
                  text.text = @"stop being silly"];
                  break;
              case 4:
                  [text.text = @"silly... silly"];
                  break;
              case 5:
                  text.text = @"what you silly boy"];
                  break;
  
             ...
              case 0:
                  text.text = @"you silly"];
                  break;
          }
  </code></pre>