NSArray vs. NSMutableArray // NSArray vs. NSDictionary

NSMutableArray (and all other classes with Mutable in the name) can be modified. So, if you create a plainNSArray, you cannot change its contents later (without recreating it). But if you create an NSMutableArray, you can change it — you'll notice it has methods like -addObject: and -insertObject:atIndex:.







In NSArray - every item in the collection has an integer index, so there is an explicit order to the items. When you're retrieving/replacing/removing the stored object from the NSARRY,you need to specify the corresponding object index of that stored object.


NSDictionary - derived from the word called entry. Each entry consists of one object that represents the key and a second object that is that key’s value. Within a dictionary, the keys are unique. That is, no two keys in a single dictionary are equal (as determined by isEqual:).When you're retrieving the object from the dictionary you need to specify the key value for the objectForKey Whenever if you're parsing the plist then NSDictionary would be ideal.You can refer apple's document here for more explanation about NSDictionary.