Value for key from NSMutableDictionary doesn't print - objective-c

Question

I'm learning "Programming in Objective-C" from Stephen Kochan and I have a problem with a mutable copy of NSDictionary.
So, here is my code:
NSMutableString *value1 = [[NSMutableString alloc ] initWithString: #"Value for Key one" ];
NSMutableString *value2 = [[NSMutableString alloc ] initWithString: #"Value for Key two" ];
NSMutableString *value3 = [[NSMutableString alloc ] initWithString: #"Value for Key three" ];
NSMutableString *value4 = [[NSMutableString alloc ] initWithString: #"Value for Key four" ];
NSString *key1 = #"key1";
NSString *key2 = #"key2";
NSString *key3 = #"key3";
NSString *key4 = #"key4";
NSDictionary *dictionary = [[NSDictionary alloc] initWithObjectsAndKeys: value1, key1, value2, key2, value3, key3, nil];
NSDictionary *dictionaryCopy = [[NSDictionary alloc] init];
NSMutableDictionary *dictionaryMutableCopy = [[NSMutableDictionary alloc] init];
dictionaryCopy = [dictionary copy];
dictionaryMutableCopy = [dictionary mutableCopy];
[value1 setString: #"New value for Key one" ];
[value2 setString: #"New value for Key two" ];
[value3 setString: #"New value for Key three" ];
dictionaryMutableCopy[key4] = value4;
NSLog(#"All key for value 4");
for (NSValue *key in [dictionaryMutableCopy allKeysForObject:value4]) {
NSLog(#"key: %#", key);
}
NSLog(#"All values");
for (NSValue *val in [dictionaryMutableCopy allValues]) {
NSLog(#"value: %#", val);
}
for (NSValue *key in [dictionaryMutableCopy allKeys]) {
NSLog(#"Key: %# value: %#", key, dictionary[key]);
}
How you see and the end of the code I'm printing all key/values from my NSMutableDictionary, but for key 4 I haven't a value!
Screen from terminal
But how you can see the value for key 4 is't null!
[Content of NSMutableDictionary][2]
What's the problem? Please help

Answer 1

In the final for loop, you are getting the value from dictionary instead of dictionaryMutableCopy:
for (NSValue *key in [dictionaryMutableCopy allKeys]) {
NSLog(#"Key: %# value: %#", key, dictionaryMutableCopy[key]);
// ^^^^^^^^^^^^^^^^^^^^^
}