title: Objective C frame animation
body: <p>Im reading a tutorial to animate sprite sheet frames in objective-C, 
  code below shows how to allocate and initialize a mutable array and loop
  through it using a for loop.</p>
  
  <pre><code>NSMutableArray *frames = [[NSMutableArray alloc]init];
      for (int i=0; i&lt;=10; i++) {
          NSString *frameName = [NSString stringWithFormat:@"a%04i.png",i];
      }
  </code></pre>
  
  <p>i can't understand how this piece of code works :</p>
  
  <pre><code>:@"a%04i.png",i
  </code></pre>
  
  <p>note that i have sprites name like this : a0001.png till ,a0031.png. simply tell me how a%4i
  works here ? thanks</p>