1. Structure is faster because it uses stack data structure while classes use heap. Stack is faster than heap. 3. We can inform it by some selectors that will tell VC which cell gets clicked. 4. By use Sync thread 5. We use singleton where we don't want to use multiple objects. For instance, in DB operations we want only one object. Its disadvantage is singleton objects will lie in the memory until the app gets terminated. So, it could produce memory issues. 6. Classes would be used where we want to inheritance. 7. API: This is the set of public types/variables/functions that you expose from your application/libraries. ABI: This is how the compiler builds an application.
It defines things (but is not limited to): * How parameters are passed to functions (registers/stack). * Who cleans parameters from the stack (caller/callee). * Where the return value is placed for return.