What is the toughest part about objective-c programming?

The toughest part about Objective C Programming is to learn Objective C itself. When you have know how and sufficient skills in Objective C, then nothing will be tough to you to go with developing Objective C Apps.

most difficult part was memory management and its been eased with ARC and there are more option for mulltithreading like GCD/operation queue. initially when i started developement and now i m pretty much confident over the thread and crashes.

thanks to Instrument features in ios (nszombies, leaks performance tools)

I think the difficult part is Memory management, altough now you can use ARC (Automatic Reference Counting). But you still need's to know about memory management for better performance of the application and to avoid crashes due to memory overload.

Every thing is tough untill you did not learn it.
Once you learn it, it becomes easy.
In initial days of my objective-c programming, I always feel memory management in objective-c is difficult -may be due to the reason I was moving from .Net to Objective-C.

The toughest part to learn about Objective-C programming is memory management. One should understand ARC (Automatic Reference Counting) to make better apps which don't crash.