iOS -- number convert to english number

This is a app is to convert number to string, so far is up to billion. For example, 101 change to one hundred one, 11 change to eleven.

Here is the view:

Here is some explanation:

1.  Define the data

2.  Here is the recursion

     NSString *prefix = [self english_num:write];

     
 To download the code from Github, here is link:

  https://github.com/MatthewLu/numberConvert