title: Unknown escape sequence "\040" in Objective-C
body: <p>I need to replace something like "abc%20def%20xyz" with "abc\ def\ xyz".
  I used this function that works fine. </p>
  
  <pre><code>string2 =[string2 stringByReplacingOccurrencesOfString:@"%20" withString:@"\ "];
  </code></pre>
  
  <p>However, I got warning saying</p>
  
  <p><code>Unknown escape sequence "\040"</code>.</p>
  
  <p>What's wrong with this, and how can I remove this  warning?</p>