referencing this post - link
I have my function declared in my header file, however the error -"Implicit declaration of function invalid in c99" still shows. I am not sure however if that is ultimately what is causing my final error which is "ld: symbol(s) not found for architecture x86_64"
I tried changing the architecture in build settings to 386, without luck.
Calling an Objective-C method looks different than calling a C function. In this instance, you've written a method
-printKthToLast:withHead:, and you'll need to call it on an object like so:
int index = [self printKthToLast:k withHead:head.next] + 1;
Note the use of square brackets around the entire method call; the receiver, in this case
self; the individual argument labels; and the lack of parentheses.