Expected identifier or '(' before #interface - objective-c

Question

First post and I am really hoping this is not a repetitive or solved question. I tried searching here and Google and while I have found similar Expected identifier or '(' errors none of the solutions work for me.
Basically I'm trying to learn Design patterns and as I used to know a bit of java I am trying to use it as an opportunity to learn objective-c so I have a java program that works and an xCode project that I get the error Expected identifier or '(' in my header file just before the #interface
this is my java solution (very simple I know):
public class Duck {
public void quack(){
System.out.print("Quack!");
}
public void swim(){
System.out.print("swimming duck!");
}
public void display(){
quack();
swim();
}
}
public class mainClass {
public static void main(String[] args){
Duck duck = new Duck();
duck.display();
}
}
and this is my objective-c version.
//duck.h
#include <CoreFoundation/CoreFoundation.h>
#interface Duck : NSObject{ //Expected identifier or '('
}
#end
// Duck.m
#include "Duck.h"
#implementation Duck
-(void)quack{
printf("Quack!");
}
-(void)swim{
printf("swimming duck!");
}
-(void)display{
[self quack];
[self swim];
}
#end
// main.c
#include <CoreFoundation/CoreFoundation.h>
#include "Duck.m"
int main(int argc, const char * argv[])
{
Duck *duck = [[Duck alloc] init];
[duck display];
return 0;
}
If any one can help I would greatly appreciate it, and again sorry if this is a duplicate post

Answer 1

The compiler doesn't know what NSObject is. If you look at the reference, you'll see that it's part of the Foundation framework, not CoreFoundation, so:
#import <Foundation/Foundation.h>
instead of:
#import <CoreFoundation/CoreFoundation.h>

Answer 2

//duck.h
//#include <CoreFoundation/CoreFoundation.h>
#import <Foundation/Foundation.h> // or Cocoa/Cocoa.h
#interface Duck : NSObject//{ //Expected identifier or '('
//} not necessary if there are no instance fields
- (void)quack;
- (void)swim;
- (void)display;
#end
// Duck.m
//#include "Duck.h"
#import "Duck.h"
#implementation Duck
-(void)quack{
printf("Quack!");
}
-(void)swim{
printf("swimming duck!");
}
-(void)display{
[self quack];
[self swim];
}
#end
// main.c SHOULD BE ~main.m~ if using ObjC!!!
//#include <CoreFoundation/CoreFoundation.h>
//#include "Duck.m"
#import "Duck.h"
Additionally, get in to the habit of using NSString literals; #"example" for if/and when you decide to advance into Cocoa. Good luck with your studies.

Answer 3

It could be that you don't really need curly brackets on your empty interface:
#interface Duck : NSObject
#end

Answer 4

Try using import instead of include. Also, make sure that the CoreFoundation framework is actually part of your project.