title: How to append a NSMutableString with a NSMutableString?
body: <pre><code>NSMutableString *str, *str1;
  </code></pre>
  
  <p>//allocation here</p>
  
  <p>i am using 
  <code>[str appendString:str1]</code> is not working.
  <code>[str appendFormat:str1]</code> is not working.</p>
  
  <p>So, how to append a <code>NSMutableString</code> with another <code>NSMutableString</code>.</p>
  
  <p><code>@str</code> is an <code>empty string</code> initialize to <code>nil</code>. <code>str1</code> has some value. <code>[str appendString str1]</code> returns <code>null</code></p>