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iOS

Posted by Daniel Davies
Daniel Davies
2,105 Points

Dynamic Typing Challenge 2

I have got through the first challenge on Dynamic Typing on Objective C basics but I just can't pass challenge 2.

The questions is:

Assign an NSNumber literal with a value of '4' to the variable 'thing'.

I have watched the video over and over and can't get this answer anywhere?

I think the closest I have got is this but it still fails:

id thing = [[NSNumber alloc] initWithInt:4];

Probably way off

Can anyone help?

5 Answers

Amit Bijlani
STAFF
Amit Bijlani
Treehouse Guest Teacher
Amit Bijlani
Amit Bijlani
Treehouse Guest Teacher

Your answer is sort of correct but you should not replace what you did in task 1. Simply add to it.

Task 1

id thing = nil;

Task 2

id thing = nil;
thing =  [[NSNumber alloc] initWithInt:4];
Chris Holloway
Chris Holloway
2,427 Points
Chris Holloway
Chris Holloway
2,427 Points

Thanks for the answer. Why doesn't this work?

id thing = nil;

NSNumber *thing = @4;

is it because thing has not been instantiated until the alloc and initWithInt methods are called?

Amit Bijlani
Amit Bijlani
Treehouse Guest Teacher
Amit Bijlani
Amit Bijlani
Treehouse Guest Teacher

You cannot declare a variable with the same name twice. With id thing = nil; you are declaring that there is a new variable named thing that is initialized to nil. On the second line, once again you are declaring a new variable thing that is of type NSNumber initialized to an object containing number 4.

You can do this:

id thing = nil;
thing =   @4;
Lucas del Río
Lucas del Río
8,768 Points

I was doing the same mistake, it's nice to know that if adding the NSNumber before the variable name 'thing' you are declaring a new variable instead of assigning a value to the existing one.

Douglas Rogers
Douglas Rogers
2,619 Points
Douglas Rogers
Douglas Rogers
2,619 Points

also there is a convenience constructor that will pass as well...

thing = [NSNumber numberWithInt:4];
Daniel Davies
Daniel Davies
2,105 Points
Daniel Davies
Daniel Davies
2,105 Points

Thanks Amit,

I had kept task 1 in place but I used id at the start of task 2 also so by removing it, it worked!

Thanks again.

Chris Holloway
Chris Holloway
2,427 Points
Chris Holloway
Chris Holloway
2,427 Points

Douglas Rogers your way is the best way to do this in my opinion.

thing = [NSNumber numberWithInt:4];