objective c - Iphone Contact list. Sort TableView view alphabetically -

I'm creating an iPhone Phonebook app that has an array of contacts (objects). I try to sort this array

But anything seems to work, I'm not sure where I will put my code in "MasterViewController". Here is part of my code

My object looks like the following

 @interface phonebookInter: person @ property NSString * firstName; @profile NSString * lastName; @ Property NSString * address; @ Property NSString * phoneNumber;   
 @end  
  @interface master VIPU controller: UITableViewController @property NSMutableArray * element; @end   
 
  @implementation MasterViewController - (id) initWithStyle: (UITableViewStyle) style {self = [super initWithStyle: style]; If (self) {} returns back to himself; } - (zero) viewDidoadload [[Super Viewedload]; Self.elements = [[NSMUTABARRRROL] INIT]; }   
 Assume that the array already contains elements. I need to sort "self.elements.lastName" array alphabetically please !!!!!!!!   
 
 
  [self Formats that sort the groups: @ [[NSSS descriptor sort descriptor with: @ "last name" ascending: yes]]];