Question: In C if we include #stdio.h we get some functions like printf, scanf. In the same way for Objective C what we should do to include NSLog,NSArray,... and where the definitions of these NSLog, NSArray are stored ? Please clarify my confusion.

Answer: 
NSLog and NSArray are both defined in Foundation.framework. In XCode cmd-click on a symbol to jump to a definition. You can add the enviroment variable DYLD\_PRINT\_LIBRARIES to your app to log Library loads on app launch.
NSLog, NSArray and other basic classes are included in Framework.h file. To import all these classes in your program simply add

`#import Framework\Framework.h`
and leave rest for the compiler.