title: How do you change the elements within an NSArray?
body: <p>I am a bit confused as to how arrays are handled in Objective-C.
  If I have an array such as </p>
  
  <pre><code>NSarray *myArray = [[NSArray alloc]
                                    initWithObjects:@"N", @"N", @"N", @"N", @"N",
                                    nil];
  </code></pre>
  
  <p>how do I change the first occurrence to "Y"?</p>