Objective C: NULL vs Nil

NULL: For C objects null pointers
Nil: For Objective C objects null pointers

But it seems they can be used interchangeably.

References

• http://stackoverflow.com/questions/557582/null-vs-nil-in-objective-c
• http://stackoverflow.com/questions/1564410/when-to-use-nil-and-null-in-objective-c
• http://stackoverflow.com/questions/2461617/are-null-and-nil-equivalent
• http://www.iphonedevsdk.com/forum/iphone-sdk-development/34826-nil-vs-null.html