Can't properly retrieve objects from NSMutableArray - ios

Question

I will be putting a variety of things in this mutable array, but first I am just trying to make sure it works by putting in strings, and then pulling out the strings. Here is my code
str1=#"1";
str2=#"2";
str3=#"3";
NSMutableArray *testArray;
[testArray addObject:str1];
[testArray addObject:str2];
[testArray addObject:str3];
retrieve =[testArray objectAtIndex:1];
NSLog(#"the test number is %#",retrieve);
The problem is that my string:retrieve equals "null" after receiving the string from the array. I'm not sure what I am doing wrong, I've looked at Apple's documentation but I'm having trouble making sense of it. I know I must be interacting with the array incorrectly, but I'm not sure how exactly. Help will be appreciated.
-Thank you!

Answer 1

You did not initialize your testArray:
NSMutableArray *testArray = [NSMutableArray array];
You can populate the array using new syntax. If you needed mutability only to add the three items, you could use a non-mutable array instead, like this:
NSArray *testArray = #[ #"1", #"2", #"3"];
If you do need mutability, call mutableCopy:
NSMutableArray *testArray = [#[ #"1", #"2", #"3"] mutableCopy];

Answer 2

Well, that's because testArray is nil. you should change the 4th line to
NSMutableArray *testArray = [NSMutableArray array];

Answer 3

You array is nil.
You are missing
NSMutableArray *testArray = [NSMutableArray array];

Answer 4

To clarify what others are telling you:
This line
NSMutableArray *testArray;
Does not create an array. It creates a pointer variable that can be used to point to a mutable array. It starts out containing a zero value (nil, points to nothing.)
It's like a postal address that points to an empty lot.
You need to create (allocate) and initialize a mutable array object in order to use it. (Continuing our analogy, you have to build a house and put a mailbox in front of it before the address becomes valid.)
So you need to say:
testArray = [#[ #"1", #"2", #"3"] mutableCopy];
Breaking that down:
The inner part,
#[ #"1", #"2", #"3"]
Creates an immutable array that contains 3 string objects.
Then we ask the immutable array to create a mutable copy of itself. We save the address of that newly created mutable array into the pointer variable testArray.
We could do it in 3 steps:
NSMutableArray *testArray;
NSArray *tempArray = #[ #"1", #"2", #"3"];
testArray = [tempArray mutableCopy];
Or all at once, like #dasblinkenlight's code:
NSMutableArray *testArray = [#[ #"1", #"2", #"3"] mutableCopy];