How can I fix this error: "The implicit declaration of the function" nslog "is incorrect on C99". say something about this error, why is this happening.
Upper / lower case is important in Objective-C, so proper use is not nslog, but nslog.
nslog
Perhaps this is due to the fact that you did not add the framework to your project.
Right-click on the top-level project folder, click Add - Exisiting Framework, and add Foundation Foundation from the list.