Unable to create mutable copy of NSDictionary - objective-c

Question

UPDATE: Now working (added fixes as suggested - Thanks!)
I've been trying to clone an NSDictionary of employee info. The main NSDictionary is created in a different class and passed along in prepareForSegue. I want to be able to create a mutable copy of that NSDictionary in another class which can then update the employee info and send it off to another class for processing so I still have the original unchanged dataset to work with at a later time. I've found a few different examples on Stack, but nothing I could get working. When I break on the btn_click method and examine the local pp object after the ..objectForKey call, pp is still nil. What have I done wrong here?
obj_person.h
#import <Foundation/Foundation.h>
#interface obj_person : NSObject
#property (strong,nonatomic) NSString *personID;
#property (strong, nonatomic) NSString *personName;
#property (strong, nonatomic) NSString *personTitle;
#end
obj_person.m
#import "obj_person.h"
#implementation obj_person
#synthesize personID = _personID;
#synthesize personName = _personName;
#synthesize personTitle = _personTitle;
#end
viewcontroller.m
#import "ViewController.h"
#import "obj_person.h"
#interface ViewController ()
#end
#implementation ViewController
int mCounter = 1;
NSMutableDictionary *mCopy;
NSMutableDictionary *mNsd;
- (void)viewDidLoad
{
[super viewDidLoad];
NSArray *arnames = [[NSArray alloc] initWithObjects:#"mary", #"jane", #"stan", #"cartman", nil];
NSArray *arkeys = [[NSArray alloc] initWithObjects:[NSNumber numberWithInt:1], [NSNumber numberWithInt:2],[NSNumber numberWithInt:3], [NSNumber numberWithInt:4], nil];
mNsd = [[NSMutableDictionary alloc] initWithCapacity:[arnames count]];
int i = 0;
for (NSString *name in arnames)
{
obj_person *p = [[obj_person alloc] init];
p.personID = [arkeys objectAtIndex:i];
p.personName = name;
[mNsd setObject:p forKey:p.personID];
i++;
}
mCopy = [mNsd mutableCopy];
}
- (IBAction)btn_click:(id)sender
{
NSLog (#"%d original items", [mNsd count]);
obj_person *pp = [mCopy objectForKey:[NSNumber numberWithInt:mCounter]];
NSLog(#"%#", pp.personName);
pp.personName = #"Gerald";
if (++mCounter > [mCopy count])
mCounter = 1;
}
#end

Answer 1

Don't define:
NSMutableDictionary *mCopy;
NSMutableDictionary *mNsd;
Outside of the #interface and #implementation. They should be instance variables, so define instance variables or use properties to define them.
It's a good job you don't use n from:
for (NSArray *n in arnames)
because it isn't an NSArray, it's an NSString. You should fix that and you should probably both name it better than n and use it.
This:
obj_person *pp = [mCopy objectForKey:[NSNumber numberWithInt:1]];
fails because the key you originally stored with is an NSString instance and the thing you are using to try to get the data out is an NSNumber instance (so they can never match).

Answer 2

You might try:
mCopy = [mNsd mutableCopy];
[mCopy retain]
One theory is that the mutableCopy returns is an autoreleased object and it's being killed off before the btn_click function fires. According to this post: Retain/release of returned objects, mutableCopy should not be autoreleasing the array, but bugs do happen.
Else, maybe try iterating through with a for-loop instead.
int cnt = [arnames count];
for(int i=0; i<cnt; i++)
...